Thank you all for your help and support on this issue.
We finally found our answer and it was an internal issue. It was a Cisco Bug, CSCvz55395. See this link:
https://quickview.cloudapps.cisco.com/quickview/bug/CSCvz55395
We had to upgrade our Firewall software from 7.0.1.1 to 7.2.5 version. This resolved the disconnects after 1 hour of logging on.
