@Huji: Perhaps that will be confusing too. Now users can see the tab and click it but nothing happens. If you do not disable it and users click they will get a message like this:
"This file cannot be transferred to Wikimedia Commons, because it is marked as رده:تصویرهای با منبع نامعلوم. Wikimedia Commons does not allow such files. This might be resolvable, but most probably means the file is not compatible. Please consult the Wikimedia Commons community policy and talk pages about licensing."
That way users will be told what the problem is and they will have an idea how to fix it. Is there a way to make the tab grey but still allow users to click it?