I'm trying everything I can to reproduce the error but it's just not happening. The only thing that's changed is that RunOnce now is .NET Framework 3.5 instead of 2.0 http://nsis.sourceforge.net/Talk:Why_do_I_get_NSIS_Error#Error_launching_installer Where is the setup located?
Apparently NSIS occurrences are to do with file corruption. http://answers.microsoft.com/en-us/windows/forum/windows_7-system/nsis-error/4e2c6938-8727-4cc8-b783-557e5d0e9f26
Fixed issue 2. UPDATE 2: Fixed issue 1. Also fixed an issue with exe files and McRipSF seemed to install fine. UPDATE 2: Test 6 release. NSIS-Error-box would have happened in the old versions but it was just hidden.