We just upgraded our server to NW6.5 SP5. Now, some machines would not let
us login. we have to shutdown and restart a few times, then we were able
to login. The next day, the same thing happened.

So, we thought we would reinstall the client. We are using 4.91 SP2. First
time uninstalling worked fine, but we couldn't reinstall, as it kept point
to an invalid drive. Then we couldn't even uninstall.

What can be the cause? Is there a fix?

Help is much appreciated.