dougiel:
Have exactly the same problem. Are you using 1.0.1 ? . I was and when I rebuilt the sketch for 0022 the problem went away !. I have no problems uploading to the other boards I have with 1.0.1 only the Mega 2560. Could it possibly be the software ?.
Dougie L
I had the same problem and also went back to 0022.
I feel fine with 022, it works great and I will not upgrade. 