I'm having trouble for the first time today, too. The message suggests I have a registration problem when I shouldn't. Is the system down? I've cleared cache, cookies, etc.
I got in yesterday and tonight I received the registration message and that I should contact member services, of course this was at 5:32 and they were closed. Has anyone else contacted MS regarding the same issue or does your membership just refresh automatically?
In case anyone really needs to check something on their DVC account, try logging in on another Disney webpage, e.g. the sweepstakes: http://disney.go.com/partners/celebrateyou/?cmp=dcom_EMC_CY_FOB__Extl
Then when you go to the DVC login you should already be logged in and can check your account. Disney has lowsy online security but in this case it is helpful.
DH just asked me to try to log in one more time and I was ABLE to get in. We were worried because we booked Xmas vacation today! Hope you all are able to get in. Good luck.