File extension not allowed?

[Birg]

I tried updating my latest UI (Druid - Legion) and got this message:

The file extension you have uploaded is not allowed. Please contact an Admin if you believe it should be allowed.

I did the exact thing I've done with all my other uploads: put WTF + Inteface + Fonts into a folder and used WinRAR to zip it to a .rar file. I even tried reuploading the current version of my UI but still got that message.

Has some rule changed since I last uploaded (28th September) or what could be the issue?

I'm not sure how to contact an admin directly hence why I'm posting here.