What version of MS.NET do you have installed? What is the complete error message? I don't see anything that you posted to suggest that Microsoft .NET is the application where the error occurred.
Do you have any of the SPs for that version installed, via critical updates at WinUpdate?
Seems to be a lot of variety for projected causes and cures...I would probably try uninstalling whatever version is installed and then reinstalling it and updating it via the WinUpdate site.
Strictly for purposes of comparison: I reflect 3 entries on Add/Remove Programs: Microsoft .NET 1.1, Microsoft .Net Hotfix, and Microsoft .NET 2.0 SP1.
Have you tried Control-Alt-Delete as a way of closing that screen?