Sunds like you have got it into your head you have to get rid of Opera michaelr.

I still can't help that feel you are being misled by the advice above.

I use 2 ISPs for internet connections and neither of them provide tech support for anything other than the most common browsers, i.e. certain IE and I think in one case also certain Netscape browsers. I can still run about 8 different browsers on 2 different platforms.

Your error message is a typical Windows "illegal operation" message and it is highly unlikely your ISP is sending something back to cause that. The chances are far higher that something in your Opera installation has got corrupted or that something in Windows itself is wrong.