I just upgraded my support library from compile \'com.android.support:appcompat-v7:23.1.1\' from compile \'com.android.support:appcompat-v7:23.1.0\'. <
compile \'com.android.support:appcompat-v7:23.1.1\'
compile \'com.android.support:appcompat-v7:23.1.0\'
Try to clean the solution and the Build it again. You might have problems with the versions of packages or dlls in your solution.