That's weird... contact SE?
Edit:
It looks like it's a billing thing, are you about to be charged for the month? If so, let it go through, then it should work.
I'm an idiot...that error message was in the "transfer other POL IDs to this SE account" option haha.
I just mocked up a transfer and I can do it. Going to triple check that my old in-game friend isn't coming back and if not I'll be Sylphin.