Sometimes Google Play store updates can cause problems with installing and/or updating Android applications - the app download process gets stuck (e.g. showing 97%) and never finishes. Occasionally errors 907 or 963 may pop up because of that too. Please check the solutions below:
1. You may need to clear cache and data of the Google Play Store app on your device:
Go to: SETTINGS --> Applications --> Application manager (or find the Google Play Store in the list) --> Google Play Store app --> Clear Cache, Clear Data
2. It is also possible to uninstall the Google Play updates and roll back the app version to fix the issue:
Go to: SETTINGS --> Applications --> Google Play Store app --> Uninstall updates
3. After that go to the Google Play Store and download GuitarTuna again.
Read here about general recommendations for troubleshooting errors 963/907. Normally, solutions explained above should help.
Please also check the Google Play Help Forum post about the problem.
Play Store won't load or download apps