A Fadal tech worked on one of my machines yesterday for the same error, only it was the Z axis. He swapped the boards too and it still happened. Then he would tap the board and would get the error. Knocking on the frame that houses the cards would also set off the error. He pulled out all of the cards, took a scribe and pushed in each contact in the motherboard slots and sprayed the contacts with cleaner. End of problem. He told me that they have had problems with some motherboards and the controller upgrade now includes the motherboard. He also noted that the cards I have appear to be thinner than some of the cards in other machines. They do move side to side quite a bit.
Hope this helps.