Token-based server access validation failed with an infras..

Hello,

I performed an upgrade from SQL 2005 to SQL 2008 on my Vista ultimate box. I
performed all the preinstallation checks and go no errors. The installation
completed with no errors. But when I open up the Database Manager and try to
connect to my local SQL database I get an "Login failed for user ***" error
number 18456. After further investigation in the event log I see that the
error is:

Login failed for user '****\****'. Reason: Token-based server access
validation failed with an infrastructure error. Check for previous errors.
[CLIENT: <local machine>]

(the **** being my user name)

I'm am getting the same error if I try to connect using the SQL 2005
Database manager, that was working just fine before the upgrade. Whats really
curious, is that if I log into a different account on my Vista box and try to
connect to the SQL server it will let me in.

Does anyone have any clue how I can correct this "infrastructure error"??

Thanks!!!