Situation : Netware 6.5 SP6 network with Zenworks 7 fully patched

When somebody log's in to the network the Client disappears and the screen stays black for about 1 minute. Some people can't wait for this tiem and think that the systems stopted and reset the computer with all problems that this gives.
I enabled the Zenwork Logfiles and can find only one problem in a file called WM1213603800:

06/16/2008 10:11:47 [78C-130] [10:11:47] WMSignalActivityEvents called!
06/16/2008 10:11:47 [78C-424] [10:11:47] Dispatch thread is alive!
06/16/2008 10:11:50 [78C-130] [10:11:50] DispatchedMonitor is alive...
06/16/2008 10:12:43 [78C-39C] [10:12:43] NWCCGetConnRefInfo failed getting authentication state: 87
06/16/2008 10:12:43 [78C-39C] [10:12:43] NDS Connections have NOT changed!
06/16/2008 10:12:47 [78C-424] [10:12:47] Dispatch thread is alive!
06/16/2008 10:13:43 [78C-39C] [10:13:43] NDS Connections have NOT changed!

Between 10:11:50 and 10:12:43 the computer wait on a authentication that doesn't works.

What to do?

Thanks,

Marcel de Jager