I got this sort of message a few times. I can't remember exactly but it happened when some general Microsoft software stopped functioning and caused a conflict with Blitz3d's compiler. The solution was to simply restart the pc.
If that's not the solution then you may have installed, or uninstalled, something that is now causing a conflict.
If that's not the solution then you may have installed, or uninstalled, something that is now causing a conflict.