I also have that email. I sent a message through Seetickets customer care to see if it was a bogus mail, but received NO REPLY ! I sent another message to them this morning but it is too late to send my tickets back and receive replacements. There doesn't seem to be a phone number to contact them on. I may try phoning Cardiff Stadium direct later today. I just know they will tell me they are helpless to do anything, the problem is between me and Seetickets.
Looks like I am going to miss out this weekend and then have a battle to get a refund.! (very disgruntled ex Dons supporter)