AppCompat v7 r21 returning error in values.xml?

Make sure the value for target (which tells the target android version) in project.properties file of both your project folder and appcompat_v7 folder is same (preferably the latest).

: inside 'your_project'/project.properties

target=android-21 android.library.reference.1=../appcompat_v7

and

: inside appcompat_v7/project.properties

target=android-21 android.library=true

and after this don't forget to clean your project .

AppCompat v21 builds themes that require the new APIs provided in API 21 (Android 5.0). To compile your application with AppCompat, you must also compile against API 21. The recommended setup for compiling/building with API 21 is a compileSdkVersion of 21 and a buildToolsVersion of 21.0.1 (which is the highest at this time - you always want to use the latest build tools).