I've currently setup a custom tab app on my fanpage - visiting this is working perfectly fine from my browser.
However when visiting the same url from my mobile, I just get some red text on Facebook saying "The page was not found".
I've defined the following (noteworthy) settings for the app:
- Namespace (which gives me a canvas page)
 - Canvas url
 - Secure canvas url
 - Page tab url
 - Secure page tab url
 
I then also tried to fill out the "Mobile site url" with the same url as the canvas url - thinking this was the missing brick? But atleast not difference.
Any ideas?