The problem is that the box hangs up and stops forwarding traffic. To get it working again it needs a cold reboot.
if you are not already running the latest 6.10 image, you should definitely upgrade.
There was in the past hangs that got fixed.
The latest image should include all these fixes.
If you have the latest image, we'll need to give you a procedure to force the CSS to crash and create a core dump.
To get this info you will habe to open a service request with the TAC.