Thanks shmem I also found the source.

The puzzling thing is, the code doesn't give that (or any other) error, when run normally. It only happens when run under the auspices of a binary debugger. Actually just an api tracer along the lines of strace.

Which implies that the debugger is modifying the contents of memory, except I can run it on any number of other apps without problems. I can even run it perl.exe running any number of other scripts without this problem.

I suspect that it has something to do with that hookey goto.