.NET for Android error XA0129

Issue

This issue happens when you are trying to use fast deployment on a device which does not support it. In this case both the normal and backup types of fast deployment failed. The Fast Deployment system makes use of the run-as feature of the Android OS. This feature was either not available or had limited capabilities in API 20 and earlier

Solution

Disable Fast Deployment by setting EmbedAssembliesIntoApk = True in your .csproj. Or turn off Fast Deployment in the IDE. You will still be able to debug on the device, all the required files will be packaged inside the .apk.