Random 403 forbidden errors on newer Workstations

[fweigert]

Here is our setup:
BM39SP1 and Surfcontrol on Netware 6.5 SP7.

Workstation Windows XP SP2
SSO timeout set to 60 seconds
No firewall on the Desktops

We are lately seeing random 403 errors for random users. Once this occurs no site will work and any access attempt will instantly produce a 403 access denied. Stopping and restarting client-trust will not work. A reboot will always fix the issue. It seems that this mostly occurs on newer machines with current MS patches (for SP2 :-)), most frequent on Dell Optiplex 755 boxes. It does however occur to randomly to reliably reproduce it at this point. Whenever it happens it's usually a Senior VP or higher :-)

Anybody have seen anything similar?

Thanks,

Frank