[Note: this does not apply to the Amazon version of the game.]

If you had unspent Glu Credits in your account that suddenly dropped to zero, OR if your game is not adding currency earned during gameplay, make sure you are playing while connected to a reliable Wi-Fi.  If the problem remains, your device may not be communicating to our servers. Here is how to resolve the problem:

What we'll do is find a folder called com.glu.android.gwallet, (/Android/Data/com.glu.android.gwallet,) and delete it.  Where it is depends upon whether you have the game installed in your device's main memory, or your SDcard (if you have an SD card.)

If your device has a file manager, use that, otherwise you can use a free one such as  "Astro" which you can download from Google Play.  

1) Under either your main device storage, or the sdcard, in the root folder you'll find the folder called "Android" and open that up. Sometimes your root folder will be called sdcard0, depending on your version of the Android operating system.

2)  Inside that folder you'll see another folder called "Data."  Open that up...

3) and now  you should see the folder called com.glu.android.gwallet   If you don't see that folder in your main memory, start over and look in your SDcard.  Delete the folder
At this point you can restart the game, and that gWallet folder will be re-created. This should re-establish your connection to Glu's servers.