Could you not re-register with the forum using your current email address - given that it doesn't seem to be recognised as an existing registered address? I don't think you have to be a Qimage purchaser to join the forum (perhaps someone else can confirm/refute). If you can thus access the forum you can take it from there.
nb there is a listing of forum members obtained via Qimage forum indexed by the user name chosen/allocated for the forum. This doesn't seem to be the same name used to purchase Qimage. Your email address will be on that list if you allowed it.