The game was most likely updated and your files might have gotten corrupted.

Please try the following steps:

1. Go to: Settings -> Applications -> Megaha:Re -> select Force Close

2. Go to: Settings -> Applications ->  Megaha:Re -> select Clear Data

3. Uninstall the  Megaha:Re app

4. Reboot your phone

5. As soon as your phone starts, direct your browser to Nutaku to download the Nutaku Android Client for automatic game updates.