Increase 250 users limit using command line

If you need to perform Load Tests in Visual Studio with more than 250 users, here is what you need to do:

1. Click Start ->  All Programs -> Microsoft Visual Studio 2010 ->Visual Studio Tools, and then right-click Visual Studio 2010 Command Prompt -> Run as Administrator.

2. Type the following command:

 VSTestConfig Licenses /AddKey:AAAAA-BBBBB-CCCCC-DDDDD-EEEEE.

Note: To get the license key:

- login to your MSDN Subscription -> My Product Keys ( https://msdn.microsoft.com/en-us/subscriptions/keys/ ) -> Visual Studio 2010 -> Visual Studio Load Test Virtual User Pack 2010  

Source:

http://msdn.microsoft.com/en-us/library/ff426121%28v=vs.100%29.aspx