After running the WLC for an extensive period of time with controller traffic going on the MBUF(controller network packet buffer) runs out and the system stops functioning and freezes.
This problem is documented in Cisco bug ID CSCsb93817.
It happens when there are numerous Dynamic Host Control Protocol (DHCP) activities going through the WLC.
There is no workaround for this issue. This problem has been fixed in WLC version 3.2(78).
To download the latest version, go to Software Download: 4100 Series WLC.
Poor connectivity / Performance
Wireless LAN Controllers
Dynamic addressing (DHCP)
sysapi_if_net.c 201: MbufGet: no free Mbufs
Lightwieght Access Point Protocol (LWAPP)