Our company is starting to use the Microsoft Test Manager a lot more to manage our testing, both manual and automated. Additionally, we've recently started on creating some new Test Controllers and Test Agents with an exotic network configuration. On one of these new Test Controllers, I've started creating Lab test runs, and been getting the error message "The build directory of the test run either does not exist or access permission is required." When you Google this error message, you get what's described in this post on MSDN. In my case, this was the former problem: the account under which the test controller was running couldn't see the build folder.
After reading that last statement, you might say "well, why didn't you check to make sure that the drop folder was in the place it should have been ?". And, I did. Sort of. Due to our network configuration and aliases, my user could see it on the expected place at the alias in my portion of the network, but the user under which the Test Controller was running (not the tests themselves as configured in the Microsoft Test Manager, but instead the Test Controller software, they're not the same user) couldn't because we have some synchronization going on. Once I logged on to the machine on which the Test Controller service was running ** AS THE USER UNDER WHICH THE TEST CONTROLLER WAS RUNNING ** and went to the network alias myself, I could finally see that the synchronization between the locations on the network that had the same alias wasn't running and the build that I expected to be there was in fact not running.