Seems like a lot of people have trouble with this error.  Here's my
solution.  I give it to the future.  Because I love you.

private void WaitAll(WaitHandle[] waitHandles) {
 if (Thread.CurrentThread.ApartmentState == ApartmentState.STA) {
   // WaitAll for multiple handles on an STA thread is not supported.
   // ...so wait on each handle individually.
   foreach(WaitHandle myWaitHandle in waitHandles) {
     WaitHandle.WaitAny(new WaitHandle[]{myWaitHandle});
   }
 }
 else {
   WaitHandle.WaitAll(waitHandles);
 }
}