Sometimes Google Drive mistakenly causes the wrong login page to appear when documents are shared with a recipient's @otago.ac.nz email address. The incorrect page is a "Google Apps for Otago" login screen, and you won't be able to log in to it using your University username and password because the University of Otago does not use Google Apps.
Ask the sender to resend the sharing invite to another email address you use that does not end in @otago.ac.nz, such as a Gmail address.