Multiple dex files define Lcom/google/android/gms/internal/zzau

I had similar problem and your question helped me solve mine and probably will help you solve yours. Problem is that you have defined:

dependencies {
...
  compile 'com.google.android.gms:play-services-cast:7.5.0'
}

and

dependencies {
...
  compile 'com.google.android.gms:play-services:7.0.+'
...
}

Since google services 7.5.0, if you’re using single modules from play services you can’t use whole play services as dependency simultaneously. Solution is to select only those services that you need instead of whole package e.g.:

instead of

dependencies {
...
  compile 'com.google.android.gms:play-services:7.0.+'
...
}

use

dependencies {
...
  compile 'com.google.android.gms:play-services-maps:7.0.+'
  compile 'com.google.android.gms:play-services-location:7.0.+'
  compile 'com.google.android.gms:play-services-gcm:7.0.+'
...
}

Also I’m not sure but probably it would be good idea to use the same version of google services in both gradle configs.