That is strange, as there is no hard limit by default. But of course, that depends on what is the launched process doing (memory consumption, handle allocation, files, etc.). Fo example, I have tested it with "notepad.exe" on my machine and I get 150 notepad.exe running if I specify 150 instances.

You can check here for a very interesting discussion on process limits: Pushing the Limits of Windows: Processes and Threads.