Error:Execution failed for task ':android:transformClassesAndResourcesWithProguardForRelease'

This bug happens when the versions of SDK, Build Tools and Gradle Plugins doesn't match (in terms of compatibility). The solution is to verify if you are using the latest versions of them. The gradle plugins are placed in the build.gradle file of the project. Other versions are in the build.gradle file of the module. For example, for SDK 23, you must use the Build Tools 23.0.1 and gradle plugins version 1.3.1.

Clean the project after changing settings. (Solved my problem, and never seen it again.)

refer this question

Remove lines from proguard-rules.txt that contains:

-injars, -outjars, or -libraryjars

and rebuild.

Removing minifyEnabled true from release config worked for me.