How to configure referenced assemblies？

I created a class library project, in which there is an abstract class
"**ScreenViewModelBase**",
I created another class library project, and established
"**ShellViewModel: ScreenViewModelBase**"
When I refer to these two class libraries in the main project, I create
"**public class AppBootstrapper: Bootstrapper**"
with exception "**no registrations found for service ShellViewModel**." so when I rewrite "**ConfigureIoC**", I add `builder. Bind(). Toallimplementation()`, the same exception will still occur, but when I no longer have cited After all the code is implemented to the main project in this way, this exception will not happen again. It seems that everything is normal again. I don't understand why? Is it related to the assembly?

Start by reproducing the reported setup with ScreenViewModelBase, ShellViewModel, AppBootstrapper, and the overridden ConfigureIoC. Compare behavior when the class libraries are referenced directly versus when their code is moved into the main project, then determine whether assembly discovery or registration causes the missing-service exception. Done means the cause is identified and the issue has a clear resolution or reproduction details.

Written by the indexing model from the issue text.