Error: failed to find target with hash string 'android-21'

Question

I want to change my compileSdkVersion from 23 to 21.So I have made following changes in the build.gradle but I am getting following error.How can I resolve this?

Answer 1

This error I also getting again and again when I import other's project. So I resolve to change some in Gradle file according to my system.

compileSdkVersion 23
buildToolsVersion "23.0.2"

Which I have already installed in my system.