Hello!
I did want make a Submission in mods.
But when i did want add a preview mods show Internal Server Error
You can view it in attached files.
I am getting the same problem man! I want to submit my first mybb theme!
I want ,too.
But i can not upload previews!!
This is likely related to recent changes server side. Chris Boulton will be addressing it shortly. Perhaps Tim B. will provide more details.