“performed an illigal operation”

Open netscape a couple of days ago and found out that i couldn’t read my mail cause there was an illigal operation and when view details it told me somethinng about page default hasn’t done somethin” When another user checks their email it is fine. I want to know what is happening with this email thing?

What really happens to trigger that Illegal operation message in any program? i have been currently getting it from MSword and Netscape, what’s going on? Need help here?