I suppose that's the reason why the veto option is there, right? You said your team was stacked, so why would you get upset at somebody not wanting you to get even better?
I can't remember ever vetoing a trade, but I can see reason behind it. Especially if a team is already stacked and basically unbeatable.
Additionally, you said you were the commish. Why did you let this cat back into the league if you knew he was going to be a trouble maker?
Anywho, good luck with your issue.