XP SP2, NWC 4.91SP4, Zen 7.0.1(ir3a), nw6.5 sp6

DLU on and set to not volatile.

Also posted in the zen forums.

We have recently gone and upgraded every PC to the above client versions. At random times people will get the windows login box after typing their NW credentials.

New users on pc's more often then not will not be able to login.

People have gone weeks w/o a problem then suddenly 2nd login box. Occasionally a reinstall of the zen client clears this up but most often not. And if it does, it doesn't last.

All latest nwc patches applied.

any ideas?