Download unsuccessful error is seems to be a common error for the entire line of Android devices.
There are steps you can take to fix the errors :
- Open Settings.
- Select Applications.
- Select Playstore (You may have to press Menu > Filter > All to see it)
- Select Clear cache.
- Back out of the screen and select Download Manager.
- Select Clear data
- Also clear data for Google Apps, Google Talk, and Checkin Service. Some users are reporting they had to clear data for the Browser app as well.
Now try again see if downloading from the Android Playstore works now.