MySpark account and XtraMail email (and what you likely use through Outlook) are different accounts, so should have different passwords. Unless you've used the same one for both...

The confusing part is that you've probably got the same email address (your @xtra.co.nz) one as the same for your email and MySpark -and your browser will save the wrong password for the other one because both sites are on spark.co.nz domain.

So it'll be trying to login to your Email with the MySpark password, and when you update that saved password with the Email one, MySpark won't work next time you try to login to that automatically.