Hey skyglow, the exam papers website prevented me from accessing it for a while with the message "your account has expired".
I rang up IT a couple of weeks ago and they said that there had been some issues with accounts, and were able to fix my problem overnight.
Your problem seems of a similar nature, so if you still can't get in, maybe just ring the Otago hotline (0800 80 80 98)?
Oh, and I'm still far from being enrolled (my status is still "awaiting confirmation from the admissions committee"). I rang up yesterday and had a bit of a rant to them, and they say that this is all normal - they just take ages to do anything because it is all manual.