As a system engeneer, I can tell you there is no valid reason, except for security software, to not accept this changed .exe
It sounds to me like your system is in bad shape and could use a reinstall.
In order to test this idea, find a friend with a computer, install and mod there, and try again. Better yet: test on a clean system. If it runs, you know what to do
If you live near Assen, PM me and I'll do it for you :p