android-support-v7-appcombat jar mismatch and app crashing after Android 4.4 SDK update-Collection of common programming errors

This error occurs when there are multiple and different instances of the same library are found in the same project, or libraries used by it. A very simple way to resolve this is use the common lib at both the places. To do so:

Just copy your C:\Users….\AppData\Local\Android\android-studio\sdk\extras\android\support\v7\appcompat\libs\android-support-v7-appcompat.jar and paste it in your libs folder, replace the old one with this. Clean the project, and it shall compile now..

Edit 1: Basically the idea is if you are using the same libraries, it shall be the common jar, or the same jar. In your case if you are using the appv7 as an external project, please go to libs folder of your project copy android-support-v4.jar, and paste into the libs of android-support-v7-appcompat project.

Also, make sure if there are other external jars or support libraries used by you, they shall be the similar jars in all the projects you are using.

I hope it helps!