I have been getting the "Windows needs your credentials" balloon in the systray. This is what I have already tried,

Run GPEDIT.MSC. Under computer configuration, expand administrative templates>system>logon. Select the "Always wait for the network at computer startup" value. The default state is "not configured". Set this to "On".

but to no avail. Anyone have any other suggestions?----Windows XPPro

After a little bit of investigation, the user that this was happening to had two active log-ons with laptops, and a desktop pc. For anyone who might run into this issue, I logged the user off of all of the computers, refreshed active directory, and logged the user back in with no trouble.