Hi
In your router config you have mentioned as ip address negotiated on the dialer interface and in the pix config you defined a static ip representing the peer(router).
Are you sure whether you are getting the same ip every time whenever you are getting connected ?
Did you try checking up with debug on the cisco router as well as on pix firewall to identify where the vpn negotiations are going wrong ?
You can make use of the below topics for debugging ...
# Configuring and Troubleshooting Cisco Network-Layer Encryption: Background - Part 1
# Configuring and Troubleshooting Cisco Network-Layer Encryption: IPSec and ISAKMP - Part 2
http://www.cisco.com/en/US/partner/tech/tk583/tk372/tsd_technology_support_troubleshooting_technotes_list.html
regds