I tried to upload a Decal. As I was said before: one .tga-file in .zip-folder and .jpg as 'screenshot'. So why does it say "There was a problem uploading the selected file"?
Not enough information to work with. I'm looking through the invalid submissions and I can't link any of them back to this poster name. So I can't comment on what might be wrong.
Let's try this again. There is nothing that has been submitted to Player Studio and deemed Invalid that is named Black Guard. What was the name of the .zip file itself?