Resolved versions for app (26.1.0) and test app (27.1.1) differ

configurations.all{
    resolutionStrategy {
        force 'com.android.support:support-annotations:26.1.0'
    }
}

Recently I was getting this error again....I just go to build->rebuild project and it works everytime for me.

Change all the implementation in your build gradle app For Example.

  implementation 'com.android.support:appcompat-v7:27.1.1'
  implementation 'com.android.support:design:27.1.1'
  implementation 'com.android.support:support-annotations:27.1.1'

Change It all to latest version(27.1.1) and sync the project.