One of my tablets does the same thing. Sometimes it works sometimes it doesn't.
If you have two or more networks in your house make sure the Mini is connected to the same network.
Make sure your receiver is in a menu screen where TV is not playing in the background. You can not watch TV and tablet at the same time.(Hint: Coming in next update. )
Try Hard resetting your Tablet.
If you don't get the Big2Small App to work try the Amiko Steamer App.
https://play.google.com/store/apps/details?id=com.amikostb.alistream
Also note if you have lots of channels scanned in it will not work either, this is a bug.
To test this stick a USB Flash Drive in your receiver and make a back-up of your channels, then reset your receiver to defaults and only scan in one sat that only has a few channels.
Try again if it works this time you know that is what is was.
I would only try this as a last resort.
I assumed Big2Small is what you were using, that is why I suggested the Amiko Steamer.Success! The Big2small App works, just not the Amiko App.