I do not know all the errors' effects of Xolox. I know that none of the simple ones (404, 403, ect.) have any noticable effect execpt the usual page that IE brings up for that error instead of what you where trying to get. Some script errors do seem to crash Xolox (there were issues with that in the past). I'm sure anything that would crash IE would cause Xolox to be dragged down with it.