I saw in the link https://groups.google.com/forum/#!topic/nunit-discuss/0wUEW1mD-S4 that Charlie answer a question with the next answer:
.NET 4.0 if necessary, using a separate process. PNUnit uses NUnit. but I think it calls NUnit at a lower level that bypasses the possibility of running in a separate process. To get around this, you might need to force the pnUnit agent to run under .NET 4.0. You can do that by setting an environment variable or by modifying the config file.
Charlie
So I want to know how to setting an enviroment variable for the agent?
Thanks, Assaf.