Can't Bind Mouse Button 1 to Player Movement.

I was messing around with the practice tool and I bound MB4 and MB5 to player attack move click so that I could practice using that, but after I used it a couple times the client unbound my basic movement of MB1 and bound it to MB2. I tried changing it back to MB1 but nothing happens to the client if I click the MB1 when it prompts me to bind a key. In fact, I can't bind anything to MB1 in the entire client. MB1 by itself just doesn't exist according to the client. I can bind shift+MB1 to player movement, but MB1 by its self does not work.

Can anyone suggest a fix to this? Game is completely unplayable without being able to the left mouse button to move.