We have 3 of these routers deployed which work perfectly with the VPN tunnel for 6-12 hours.  The units after this time period will drop the VPN tunnel, but will still work with the Internet.  If the router is power cycled, it will immediately reconnect to the VPN.  Here is what we are seeing in the log:

VPN Log 
Type:   ALL System Log ACL Log Firewall Log VPN Log    
Mar 5 06:57:24 - [VPN Log]: "TunnelName" #1819: Informational Exchange message must be encrypted
Mar 5 06:57:24 - [VPN Log]: "TunnelName" #1819: Informational Exchange message must be encrypted
Mar 5 06:57:26 - [VPN Log]: "TunnelName" #1796: Informational Exchange message must be encrypted
Mar 5 06:57:27 - [VPN Log]: "TunnelName" #1800: Informational Exchange message must be encrypted
Mar 5 06:57:29 - [VPN Log]: "TunnelName" #1808: Informational Exchange message must be encrypted
Mar 5 06:57:29 - [VPN Log]: "TunnelName" #1804: Informational Exchange message must be encrypted
Mar 5 06:57:31 - [VPN Log]: "TunnelName" #1817: Informational Exchange message must be encrypted
Mar 5 06:57:31 - [VPN Log]: "TunnelName" #1812: Informational Exchange message must be encrypted
Mar 5 06:57:34 - [VPN Log]: "TunnelName" #1819: Informational Exchange message must be encrypted
Mar 5 06:57:34 - [VPN Log]: packet from XXX.XXX.XXX.XXX:500: ignoring informational payload, type INVALID_COOKIE
Mar 5 06:57:34 - [VPN Log]: packet from XXX.XXX.XXX.XXX:500: received and ignored informational message
Mar 5 06:57:36 - [VPN Log]: "TunnelName" #1794: Informational Exchange message must be encrypted
Mar 5 06:57:41 - [VPN Log]: packet from XXX.XXX.XXX.XXX:500: ignoring unknown Vendor ID payload [5b362bc820f60007]
Mar 5 06:57:41 - [VPN Log]: packet from XXX.XXX.XXX.XXX:500: received Vendor ID payload [RFC 3947] method set to=109
Mar 5 06:57:41 - [VPN Log]: packet from XXX.XXX.XXX.XXX:500: received Vendor ID payload [draft-ietf-ipsec-nat-t-ike-03] meth=108, but already using method 109
Mar 5 06:57:41 - [VPN Log]: packet from XXX.XXX.XXX.XXX:500: received Vendor ID payload [draft-ietf-ipsec-nat-t-ike-02_n] meth=106, but already using method 109
Mar 5 06:57:41 - [VPN Log]: packet from XXX.XXX.XXX.XXX:500: received Vendor ID payload [draft-ietf-ipsec-nat-t-ike-00]
Mar 5 06:57:41 - [VPN Log]: "TunnelName" #1823: responding to Main Mode
Mar 5 06:57:41 - [VPN Log]: "TunnelName" #1823: transition from state STATE_MAIN_R0 to state STATE_MAIN_R1
Mar 5 06:57:41 - [VPN Log]: "TunnelName" #1823: STATE_MAIN_R1: sent MR1, expecting MI2
Mar 5 06:57:41 - [VPN Log]: "TunnelName" #1823: ignoring unknown Vendor ID payload [404bf439522ca3f6]
Mar 5 06:57:41 - [VPN Log]: "TunnelName" #1823: received Vendor ID payload [XAUTH]
Mar 5 06:57:41 - [VPN Log]: "TunnelName" #1823: ignoring unknown Vendor ID payload [da8e937880010000]
Mar 5 06:57:41 - [VPN Log]: "TunnelName" #1823: received Vendor ID payload [Dead Peer Detection]
Mar 5 06:57:41 - [VPN Log]: "TunnelName" #1823: NAT-Traversal: Result using 3: no NAT detected
Mar 5 06:57:41 - [VPN Log]: "TunnelName" #1823: transition from state STATE_MAIN_R1 to state STATE_MAIN_R2
Mar 5 06:57:41 - [VPN Log]: "TunnelName" #1823: STATE_MAIN_R2: sent MR2, expecting MI3
Mar 5 06:57:41 - [VPN Log]: "TunnelName" #1823: ignoring informational payload, type IPSEC_INITIAL_CONTACT
Mar 5 06:57:41 - [VPN Log]: "TunnelName" #1823: Main mode peer ID is ID_IPV4_ADDR: 'XXX.XXX.XXX.XXX'
Mar 5 06:57:41 - [VPN Log]: "TunnelName" #1823: I did not send a certificate because I do not have one.
Mar 5 06:57:41 - [VPN Log]: "TunnelName" #1823: transition from state STATE_MAIN_R2 to state STATE_MAIN_R3
Mar 5 06:57:41 - [VPN Log]: "TunnelName" #1823: STATE_MAIN_R3: sent MR3, ISAKMP SA established {auth=OAKLEY_PRESHARED_KEY cipher=oakley_3des_cbc_192 prf=oakley_sha group=modp1024}
Mar 5 06:57:41 - [VPN Log]: "TunnelName" #1823: cannot respond to IPsec SA request because no connection is known for 192.168.18.0/24===XXX.XXX.XXX.XXX[S?C]...XXX.XXX.XXX.XXX[S?C]===192.168.4.0/24
Mar 5 06:57:41 - [VPN Log]: "TunnelName" #1823: sending encrypted notification INVALID_ID_INFORMATION to XXX.XXX.XXX.XXX:500
Mar 5 06:57:42 - [VPN Log]: "TunnelName" #1824: responding to Quick Mode {msgid:783c81f7}
Mar 5 06:57:42 - [VPN Log]: "TunnelName" #1824: transition from state STATE_QUICK_R0 to state STATE_QUICK_R1
Mar 5 06:57:42 - [VPN Log]: "TunnelName" #1824: STATE_QUICK_R1: sent QR1, inbound IPsec SA installed, expecting QI2
Mar 5 06:57:42 - [VPN Log]: "TunnelName" #1823: Informational Exchange message must be encrypted
Mar 5 06:57:50 - [VPN Log]: "TunnelName" #1793: max number of retransmissions (20) reached STATE_QUICK_R1
Mar 5 06:57:50 - [VPN Log]: "TunnelName" #1798: Informational Exchange message must be encrypted
Mar 5 06:57:51 - [VPN Log]: "TunnelName" #1814: Informational Exchange message must be encrypted
Mar 5 06:57:51 - [VPN Log]: "TunnelName" #1806: Informational Exchange message must be encrypted
Mar 5 06:57:51 - [VPN Log]: "TunnelName" #1802: Informational Exchange message must be encrypted
Mar 5 06:57:51 - [VPN Log]: "TunnelName" #1810: Informational Exchange message must be encrypted
Mar 5 06:57:52 - [VPN Log]: "TunnelName" #1823: Informational Exchange message must be encrypted
Mar 5 06:57:52 - [VPN Log]: "TunnelName" #1819: Informational Exchange message must be encrypted
Mar 5 06:57:54 - [VPN Log]: "TunnelName" #1819: Informational Exchange message must be encrypted
Mar 5 06:58:04 - [VPN Log]: "TunnelName" #1821: max number of retransmissions (2) reached STATE_QUICK_I1. No acceptable response to our first Quick Mode message: perhaps peer likes no proposal
Mar 5 06:58:06 - [VPN Log]: "TunnelName" #1796: Informational Exchange message must be encrypted
Mar 5 06:58:07 - [VPN Log]: "TunnelName" #1800: Informational Exchange message must be encrypted
Mar 5 06:58:09 - [VPN Log]: "TunnelName" #1804: Informational Exchange message must be encrypted
Mar 5 06:58:09 - [VPN Log]: "TunnelName" #1808: Informational Exchange message must be encrypted
Mar 5 06:58:10 - [VPN Log]: packet from XXX.XXX.XXX.XXX:500: ignoring informational payload, type INVALID_COOKIE
Mar 5 06:58:10 - [VPN Log]: packet from XXX.XXX.XXX.XXX:500: received and ignored informational message
Mar 5 06:58:11 - [VPN Log]: "TunnelName" #1812: Informational Exchange message must be encrypted
Mar 5 06:58:11 - [VPN Log]: "TunnelName" #1817: Informational Exchange message must be encrypted
Mar 5 06:58:12 - [VPN Log]: "TunnelName" #1823: Informational Exchange message must be encrypted
Mar 5 06:58:16 - [VPN Log]: "TunnelName" #1795: max number of retransmissions (20) reached STATE_QUICK_R1
Mar 5 06:58:30 - [VPN Log]: "TunnelName" #1798: Informational Exchange message must be encrypted
Mar 5 06:58:31 - [VPN Log]: "TunnelName" #1810: Informational Exchange message must be encrypted
Mar 5 06:58:31 - [VPN Log]: "TunnelName" #1802: Informational Exchange message must be encrypted
Mar 5 06:58:31 - [VPN Log]: "TunnelName" #1806: Informational Exchange message must be encrypted
Mar 5 06:58:31 - [VPN Log]: "TunnelName" #1814: Informational Exchange message must be encrypted
Mar 5 06:58:32 - [VPN Log]: "TunnelName" #1819: Informational Exchange message must be encrypted
Mar 5 06:58:34 - [VPN Log]: "TunnelName" #1822: max number of retransmissions (2) reached STATE_QUICK_I1. No acceptable response to our first Quick Mode message: perhaps peer likes no proposal
Mar 5 06:58:41 - [VPN Log]: packet from XXX.XXX.XXX.XXX:500: ignoring unknown Vendor ID payload [5b362bc820f60007]
Mar 5 06:58:41 - [VPN Log]: packet from XXX.XXX.XXX.XXX:500: received Vendor ID payload [RFC 3947] method set to=109
Mar 5 06:58:41 - [VPN Log]: packet from XXX.XXX.XXX.XXX:500: received Vendor ID payload [draft-ietf-ipsec-nat-t-ike-03] meth=108, but already using method 109
Mar 5 06:58:41 - [VPN Log]: packet from XXX.XXX.XXX.XXX:500: received Vendor ID payload [draft-ietf-ipsec-nat-t-ike-02_n] meth=106, but already using method 109
Mar 5 06:58:41 - [VPN Log]: packet from XXX.XXX.XXX.XXX:500: received Vendor ID payload [draft-ietf-ipsec-nat-t-ike-00]
Mar 5 06:58:41 - [VPN Log]: "TunnelName" #1825: responding to Main Mode
Mar 5 06:58:41 - [VPN Log]: "TunnelName" #1825: transition from state STATE_MAIN_R0 to state STATE_MAIN_R1
Mar 5 06:58:41 - [VPN Log]: "TunnelName" #1825: STATE_MAIN_R1: sent MR1, expecting MI2
Mar 5 06:58:41 - [VPN Log]: "TunnelName" #1825: ignoring unknown Vendor ID payload [404bf439522ca3f6]
Mar 5 06:58:41 - [VPN Log]: "TunnelName" #1825: received Vendor ID payload [XAUTH]
Mar 5 06:58:41 - [VPN Log]: "TunnelName" #1825: ignoring unknown Vendor ID payload [da8e937880010000]
Mar 5 06:58:41 - [VPN Log]: "TunnelName" #1825: received Vendor ID payload [Dead Peer Detection]
Mar 5 06:58:41 - [VPN Log]: "TunnelName" #1825: NAT-Traversal: Result using 3: no NAT detected
Mar 5 06:58:41 - [VPN Log]: "TunnelName" #1825: transition from state STATE_MAIN_R1 to state STATE_MAIN_R2
Mar 5 06:58:41 - [VPN Log]: "TunnelName" #1825: STATE_MAIN_R2: sent MR2, expecting MI3
Mar 5 06:58:42 - [VPN Log]: "TunnelName" #1825: ignoring informational payload, type IPSEC_INITIAL_CONTACT
Mar 5 06:58:42 - [VPN Log]: "TunnelName" #1825: Main mode peer ID is ID_IPV4_ADDR: 'XXX.XXX.XXX.XXX'
Mar 5 06:58:42 - [VPN Log]: "TunnelName" #1825: I did not send a certificate because I do not have one.
Mar 5 06:58:42 - [VPN Log]: "TunnelName" #1825: transition from state STATE_MAIN_R2 to state STATE_MAIN_R3
Mar 5 06:58:42 - [VPN Log]: "TunnelName" #1825: STATE_MAIN_R3: sent MR3, ISAKMP SA established {auth=OAKLEY_PRESHARED_KEY cipher=oakley_3des_cbc_192 prf=oakley_sha group=modp1024}
Mar 5 06:58:42 - [VPN Log]: "TunnelName" #1825: cannot respond to IPsec SA request because no connection is known for 192.168.18.0/24===XXX.XXX.XXX.XXX[S?C]...XXX.XXX.XXX.XXX[S?C]===192.168.4.0/24
Mar 5 06:58:42 - [VPN Log]: "TunnelName" #1825: sending encrypted notification INVALID_ID_INFORMATION to XXX.XXX.XXX.XXX:500
Mar 5 06:58:42 - [VPN Log]: "TunnelName" #1826: responding to Quick Mode {msgid:eae2f049}
Mar 5 06:58:42 - [VPN Log]: "TunnelName" #1826: transition from state STATE_QUICK_R0 to state STATE_QUICK_R1
Mar 5 06:58:42 - [VPN Log]: "TunnelName" #1826: STATE_QUICK_R1: sent QR1, inbound IPsec SA installed, expecting QI2
Mar 5 06:58:42 - [VPN Log]: "TunnelName" #1825: Informational Exchange message must be encrypted
Mar 5 06:58:46 - [VPN Log]: "TunnelName" #1797: max number of retransmissions (20) reached STATE_QUICK_R1
Mar 5 06:58:47 - [VPN Log]: "TunnelName" #1800: Informational Exchange message must be encrypted
Mar 5 06:58:49 - [VPN Log]: "TunnelName" #1808: Informational Exchange message must be encrypted
Mar 5 06:58:49 - [VPN Log]: "TunnelName" #1804: Informational Exchange message must be encrypted
Mar 5 06:58:51 - [VPN Log]: "TunnelName" #1817: Informational Exchange message must be encrypted
Mar 5 06:58:51 - [VPN Log]: "TunnelName" #1812: Informational Exchange message must be encrypted
Mar 5 06:58:52 - [VPN Log]: "TunnelName" #1825: Informational Exchange message must be encrypted
Mar 5 06:58:52 - [VPN Log]: "TunnelName" #1823: Informational Exchange message must be encrypted 

I am lost as to why this is happening, any assistance would be most appreciated.