Quoted from beelzeboob:Okay...real answer:
Check the threads on the bolt and/or swap out another bolt and see if it works. If it still doesn't, you may have inadvertantly stripped the threads on the leg brace inside the cabinet. Those are really the only two reasons that would be happening...unless for some reason the hole is misaligned. Check it with a flashlight.
Run a tap through it. sounds like there's some metal shavings in there