http://code2care.org/pages/parsing-data-for-android-21-failed-unsupported-major.minor-version-51.0/
Error Message :
Multiple Problems have occurred
"Loading data for
Android 5.0" has encountered a problem.
Parsing Data for android-21 failed
unsupported major.minor version 51.0
Parsing Data for android-21 failed
unsupported major.minor version 51.0

You may get this error message if you have added Android 5.0 SDK foreclipse (Android ADT)
Reason :
-
Check your Java version,
Android SDK 5.0 (API 21) requires JDK 1.8.
Solution :
Install JDK 1.8 and set java 1.8 to your eclipse and you may not get this error message.