In the past when the -2 AP error would occur, it could usually be solved by means of clearing your internet cache and restarting your computer. However, several players who have tried this recently have reported that it didn't work for them.
An Anecdote Which May Help:
I bought an Aeria Fun Card
at Target recently, after all of these reports of trouble.
I entered my code, got the notice that it worked and so on, and then went to the Web Item Mall, where, lo and behold, I saw a balance of -2 AP.
I decided to be lazy and not clear my cache, but to attempt a few other methods of resolving the situation instead. Refreshing the page had worked on some occasions in the past, but it did no good for me on this occasion. I waited, as this has also helped some in the past.
I went back to the Web IM, still -2 AP. I refreshed the page again. Still no joy. I waited some more.
I went back again to the Web IM and still had -2 AP, so, on a lark, I went to my AP Recharge History page
and saw the balance that was supposed to be there. Then I immediately went back to the Web IM and saw the correct balance.
This morning in the SB, someone reported the -2 AP balance glitch, so I sent him directly to his Aeria Points Recharge History page: https://billing.aeriagames.com/report/in_list.asp
and asked him to let me know if it fixed the problem. He said it did.