The path you're trying to execute has to be enclosed in quotes in your command line.
The command line you appear to be trying to execute is:
cmd /c C:\PROGRA~1\My App 4\Compare\app.exe
What you need to be executing is:
cmd /c "C:\Program Files\May App 4\Compare\app.exe"
Any path that has spaces in it must be enclosed in quotes.
So, the quick'n'dirty method of setting your Path would be
string Path = "\"C:\\Program Files\\My App 4\\Compare\app.exe\"";