Internet Explorer Runtime Error

I have recently started getting an intermittant Runtime Error when moving from one internet site to another. The message is “Error: A Runtime Error has occurred. Do you wish to Debug? Line:1 Error: Invalid character.” I have deleted temporary internet files and history but this didn’t help. I’ve also scanned for viruses and found none. Specifics of my computer are:
1.7 Pentium; 512 MB Ram; XP Professional 2002; Internet Explorer 6.0; Any suggestions on how to fix?