The problem has been fixed and you can now create proofs again.
The issue was caused by a refactor of the code that converts the PDF into the set of images that are actually sent to your browser for each page. The new version was incorrectly reusing a template including the details of the previous email, including its addressees. We're adding tests to avoid this happening again in the future.
Thanks for your patience.
Posted Mar 11, 2016 - 12:40 GMT
We've had a problem with this morning's release that has caused duplicate email to be sent out when proofs are created. We're working on a fix at the moment, and have temporarily disabled proof creation while we work.
I'm very sorry for any delays this causes with your work.