Some users sporadically can't connect to TMG

HI

I have a TMG Server 2010 (Version: 7.0.9193.540 Rollup 2 for TMG 2010 SP2)

The problem is thatonlysome users or computer clients loseconnectionto server and can notbrowse on interent or do a PING toTMG server, this problem is solvedautomatically after a few minutes or even hours. I found a way to solve the problem immediately, doing a PING from TMG to client, after PING works fine, connection is restablished.

This problem happends sporadically.

Any idea how to solve this problem??

thanks

LFF