exchange 5.5 owa hangs on logon page

Hello, any ideas?

Environment: W2K server sp4 and IIS5.0 w/ current

critical updates. OWA from Exchange 5.5 w/ sp4.

Exchange 5.5/NT backend. This has been up and running

problem free almost two years.

Problem: In the last month a problem has developed where

the Gold page stops responding. This can happen in one of

two ways. The page come up blank (not gold) or the Gold

page come up and hang after the user enters their

username.

Neither the IIS nor the event logs provide any clue. I

have already tried deleting the WebTemp files. A reboot

corrects the issue but it will reoccur anything between

several hours or days.
thanks,
Fatmann