Sounds like there is a burr in the threads on the lower, or either the lower or buffer tube was not made with the standard pattern threading that most everyone else uses. But most likely it is a burr. I would suggest taking them both to a local gun smith and seeing if he can find and fix the issue.

Devon, Is your Tube roll thread or point cut? If the Tube is point cut it's a commercial aftermarket tube and might not fit a Mil-Spec Lower. Just wondering... I also had the same issue with a PWS buffer.. it was just a bit "out of spec".. Nothing I could do so I sent it back.. I suppose you could tap the lower receiver if you had the right tap.. or clean up the threads on the buffer tube. No other real options.