Errorprotector is most likely leaked through your Active X controls in IE as evidenced here:
http://www.cb7tuner.com/vbb/showthread.php?p=965040 "C:\Documents and Settings\******\Local Settings\Temp\Install-Errorprotector-Free.exe ->"

Your spyware programs wouldn't detect it until it executes. Often times, it will install other files into the C:/ (right there, or it will install them in your windows system folder). If you are clean and sort by date, the nasties will be at the bottom and usually with some oddball file name like "sk239dkdm22e.exe"