If when you launch ArtRage, you are asked to validate it every time, or can only run it when connected to the internet, this is likely due to a problem with the Google Play Store license for ArtRage. Try the following steps to correct the problem.
The Google Play Store app and the Google Play Services app sometimes have caching issues which can prevent users to install or validate an app. This can usually be resolved by clearing both those app's cache and data:
Open the Settings application on your device.
Head Over to Apps Menu.
Find the Application you want to Clear the App Data of.
Select it, Move to the Storage Tab.
Hit Clear Storage/ Clear App Data.
If this doesn’t work, save your current painting to prevent data loss, then close ArtRage completely. Clear ArtRage’s app data via the Android Application Manager in Settings.
Uninstall ArtRage and reinstall. Make sure you are connected to wifi and launch ArtRage again to validate your license.