Why does Visual Studio debug on iOS device fail with can't find type?

I have a project that I can debug fine on the iOS Simulator. I have been trying to debug it on an actual device with no luck.
The app builds and installs on the device but when it launches I get an error when it tries to read the first line in my app.xaml resources dictionary:
<vm:ViewModelLocator x:Key="ViewModelLocator" />
vm is a defined namespace that uses my Core project.

Im not sure why it can't find the type ViewModelLocator, it works fine in the simulator and I have link all assemblies checked in the build options for the debug on device configuration.

Has anyone else run into something similar?

Thanks.