When you have a very large load test (file size exceeds about 100MB) the load test will not run. You get this error instead:

Test Results
Load Test Tests
Fail - 0 tests passed out of total 0 executed. Executed on ‘xxxxxx’ machine, A
Unable to pass test [LoadTest] to controller System.Threading.Tasks.TaskCanceledException: A task was canceled.
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccess(Task task)
d_O.MoveNext()

Small load tests run on the same machine work as expected.