Joel,

Do you have the aluminum tail block? If so, it may be that you've stripped the inner part of the bar inside the aluminum tail block. I would recommend that you go into your spare parts bag and get the longer screw. If you don't have this, you can purchase an Align screw set which will have the right part. I had this problem and was able to get a replacement bar for the tail block from one of the online shops I use.

I hope that helps.

Joe