Why can I build the apk but I can't build and run?

I would like to increase my productivity so I would like to be able to build and run so that I don't have to manually copy the apk over to the phone.

I get the following errors:

Error building Player: FormatException: Input string was not in the correct format

FormatException: Input string was not in the correct format System.Int32.Parse (System.String s) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System/Int32.cs:632) System.Convert.ToInt32 (System.String value) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System/Convert.cs:1270) UnityEditor.Android.PostProcessAndroidPlayer.FindDevice ()

I am new to unity and coding and I havent touched any scripts. My application uses Vuforia 5.5 and I'm on the 32 bit version of Unity 5.3.5 since Vuforia doesn't officially support the 64 bit version. I created a 'hello world' app in Android Studio to test the ABD functionality and that worked fine.

What could the problem be?

Thanks very much for any assistance.