In the world Spahn I just had a trade nullified because one of the players had "recently signed a long term contract". I have made trades previously in other worlds where the deal was to sign the player and them trade him so that the team he was going to didn't get stiffed trading top prospects for a solid vet who decided to go free agent and wouldn't sign with his new team. Is this something new since the latest "re-boot" or am I missing something somewhere? I really needed that trade to go through and it was agreed to by both owners and initiated before the trade deadline.

A contract change to a player involved in an accepted and pending trade will nullify the trade. I'm guessing that's what happened here. You made the deal, and then the LT contract was offered while the trade was pending.

The LT contract needs to be done before the trade.