How new is your copy? If it's newer than a couple of years ago it's already patched, which would be why it won't let you patch it. If it's older you can get a fully patched protection-free copy cheap.
http://www.amazon.com/Encore-16560-S...5251409&sr=1-5
I you choose that route click the Subsim Amazon link in my sig before ordering. That way Subsim.com gets a cut.