Microsoft .Net framework error msg

Just looking for some advice on this Microsoft net Framework error msg:

Unhandled exception has occurred in your application. If you click
Continue, the application will ignore this error and attempt to
continue. If you click Quit, the application will close immediately.

String was not recognized as a valid Date Time.

Bit of bkground, I have a new laptop (Vista) which started behaving erratically at start up showing alot of .dll errors. I read thru loads of forums and ended up installing and running AVG, Spybot and then following thru the Malware Removal Guide from the malware removal forum. Turns out I had a bunch of viruses (which were removed) and afterwards it seemed to be running great and all the start up errors disappeared....except for the error msg above.

I had another look thru the forums and tried out a few suggestions:
Downloaded Microsoft .Net Framework 2.0 and tried to install....wasn't able to and got this msg Errorroduct already installed (as part of the operating system)
So I uninstalled Microsoft .Net Framework 1.1 and used the .netfx clean up tool that had been suggested on another forum and tried to install 2.0 again but got the same Error msg

There's these details about enabling an HJT debugger, but I didn't really understand what I was supposed to do and couldn't find any info.....:

************** JIT Debugging **************
To enable just-in-time (JIT) debugging, the .config file for this
application or computer (machine.config) must have the
jitDebugging value set in the system.windows.forms section.
The application must also be compiled with debugging
enabled.

For example:

<configuration>
<system.windows.forms jitDebugging="true" />
</configuration>

When JIT debugging is enabled, any unhandled exception
will be sent to the JIT debugger registered on the computer
rather than be handled by this dialog box.


Any help would be great, I'm new at this!!!! :confused