Although, to be fair, jk2mp.exe is a different program from jk2sp.exe. It's entirely plausible that one could cause an error and the other, not.
Having said that, I ain't got a scooby what the cause is, sorry
If it's any consolation, it looks like a Windows problem as opposed to a JK2 error, yeah. Have you tried installing the patch?
Once you change the structure of the program, Windows may well run it alright.