I'd like to say I had an answer for you, but I'm not so sure...
The DX3 binds for me fairly easily, as long as you put both the Tx and the Rx in binding mode (and not just the Rx etc).
What I havent done is re-bind the same receiver to the Tx again.. not sure how that would go.
Is this an Rx that was previously bound to the Tx ?
-Mark