VS2010 Beta2 comes with a default license of only 250 virtual users per client. So, if you want to run a load test that needs to simulate more than 250 virtual users, you need to install an additional VU pack.

As written in Ed’s blog, the easiest way to install an extra VU pack is to install a controller and agent on the box. You can also install many agents on the same box or different m/cs.

To  add virtual users, start a Visual Studio Command prompt as Administrator (on Vista or Win7, just type Visual Studio Command Prompt in the search window, on XP you’ll find this under the Visual Studio group in the start menu). Then run this command line:

TestControllerConfig licenses /addkey:V10000

This will license the controller for 10,000 virtual users. Note that this license is temporary, and will only work in beta2. For RTM, we will only offer the 1,000 user license pack. If you have a Volume License, you will be able to get your license key from the volume licensing site, and then enter a count of licenses you want to install.

Once you have a virtual user license installed, that license can also be used for local runs (that is, the runs do not have to go through the controller).

If you just want to do local runs, and not use the controller and agent, you can run this from the command line to install the virtual user license:

VSTestConfig licenses /addkey:V10000

This enables you to exceed 250 users for local runs, and unlocks all the cores on your CPU. Pretty cool, eh?