Board Thread:Support Requests - Getting Started/@comment-24209457-20131124152618/@comment-452-20131206153604

By "Permission Error", they are most likely referring to MediaWiki:Badaccess. (Default text: Permission Error)

When using one of the 4 modal upload methods, this message is shown for ALL errors, while using Special:Upload will show custom errors.

Additionally, even on Special:Upload, all uploads blocked by MediaWiki:Titleblacklist show MediaWiki:Titleblacklist-forbidden-edit instead of MediaWiki:Titleblacklist-forbidden-upload (Unless errmsg is used to specific a custom error message - which is shown on Special:Upload, and not on modal uploaders)

Wikia Staff have been aware of these problems since at least August.