runtime erro/debug

[losixxx]

hi
hope some of you pc bod's can help

over the last few day's i keep getting runtime errors, saying

runtime error has occured do you wish to debug.

A. whats a runtime error

B. how do i get rid?

this doesnt happen on all websites i use but has just started to do it on oople tonight
tried running several virus/trojan scanners all come up clean

hope you can help as its starting to p*** me off