I had an interesting error crop yesterday on a production server that was only happening there, and not in development and QA. I was using a semaphore to throttle the number of threads that could enter a critical section on code and on this particular machine I was getting this run-time error begin thrown by the framework: "System.MissingMethodException: Method not found: 'Boolean System.Threading.WaitHandle.WaitOne(Int32)'" After a bit of googling, the best answer I could come up with is that this method was introduced in the .Net Framework 2.0 SP2. To muddy the waters a little more, you cannot download...