Hi Ichbin, I missed your reply. I've been through the list of email addresses, noticed one or two were missing @ symbols. (It was a prepopulated list that someone else had used, I've been through and set them all into the right format.
I've reuploaded this list and tested registrations again, still getting the error when I use an address not in the blacklist. I checked for any spaces, didn't catch any. Even tried find on ', @' etc.
I've only got emails in the blacklist. The whitelist is empty. As it's supposed to be.