Using Vista 64-bit Business Edition with SP1.

I want to login to a tree by using the red N icon -> Novell Login.

I can click the "Trees" button and select a tree, then the "Contexts"
button and so on.

After entering the username and the switching to the password field by
clicking in it or pressing the <tab> button, the window "flashes" and
everything from tree and context fields disappears.

Result: Can't login.

I have tried to uninstall the Client and then reinstall but it didn't help.

Any ideas what could be the problem?