Many errors like this are caused by spyware.  Have you scanned for and removed all spyware?  if not, download, install, update, and run the free versions of Ad-Aware and Spybot and let these programs remove all of the garbage that they find.

http://www.lavasoftusa.com Ad-Aware

http://www.safer-networking.org/index.php?page=download Spybot

If these programs don't solve the problem, go to the following site and follow the directions to download and run the analysis tool called HijackThis.

http://tomcoyote.com/hjt/

Generate a log file, then open it and copy and paste the text of the log file in a message in one of the following forums:

http://subratam.org/
http://www.zerosrealm.com/forums/
http://www.bleepingcomputer.com/

where a certified HijackThis expert can offer advice on how to fix the problem:

Steve