KIX 4.0x do not check the group membership at each logon. It is cached in the registry and is updated every 30 days by default. You can force the update at each logon by setting the "-f" parameter when launching kix in your batch file:

%0\..\kix32.exe %0\..\login.kix -f

This is a new behaviour in versions 4.0x. I think everybody should force the group membership update to avoid problems, for example when you create new groups -> IF INGROUP may not work at next logon, but after a few days. Hum hum..
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SAVE THE WORLD - PROTECT THE PLANET