Board Thread:General Discussion/@comment-5734178-20140505063456/@comment-452-20140506155220

"Permission error" is the default text of MediaWiki:Badaccess, this message appears if any errors occur when using one of the inline uploaders. (either on the edit page, or sidebar)

Special:Upload gives much more detailed error messages, and you should direct everyone to use that page instead, especially if they get "Permission error".

I have no idea why the same error messages are not shown.