My taxes have been rejected because my ex husband claimed our children on his taxes and shouldn't have. It's not some simple mistake, he knows he is not entitled to claim them and it has been explained to him by an attorney. I know I'll paper file and my taxes will be fine but I'm curious as to what happens to the other party? Are there ramifications for this? Is there anyway to keep it from happening in the future? (This is the 2nd year he's tried it, last year he chose not to file when caught in the midst of this)

Sometimes IRS takes a stand; sometimes it does not. I've seen amended returns filed with no ramifications. I do know if he owes taxes because of the incorrect filing he will now have to pay those taxes PLUS penalty and interest.