I had not logged in to Ax 2009 in months and the client failed to start.  I received the frame of the app, the Microsoft Dynamics AX 2009 splash screen and even the 'Welcome message".

After reinstalling the client and trying the login from different machines I performed a Run As to see if I could log in with the account I used to set up AX 2009.

This worked.  My user account information in the AX 2009 database somehow became horked up.

Solution:

Not pretty.  Delete the account and recreate it.

Issues:

The client I used to delete the account locked solid for several hours while performing the delete.

I think this is a bug in Ax 2009 as my user account was VERY rarely used and had no customizations.