Fixed deadlocking issue by removing ReaderWriterLock and replacing with lock expressions

The previous pull request I sent worked just find on my work PC, but I ran into deadlocking issues on my laptop.  I really don't understand why I'm getting a deadlock, but after reading the docs for ReaderWriterLockSlim I don't think its a good fit for this scenario anyway.  I replaced it with a simple lock statement around both methods and my deadlocking issues went away.  I think this is probably a better fix for the problem.