Found the issue! Posting here as it may help someone someday.
My web.config contains a service activation element with a factory attribute like this:
<serviceHostingEnvironment>
<serviceActivations>
<add relativeAddress="MyService.SvcImpl.svc"
service="MyService.SvcImpl"
factory="MyCompany.MyServiceHostFactory, MyCompany.MyAssembly, Version=1.0.0.0, Culture=neutral, PublicKeyToken=" />
</serviceActivations>
</serviceHostingEnvironment>
The factory attribute contains a class reference from a strongly named assembly. However, the PublicKeyToken atribute was supposed to be set by the build system to the correct value, depending on whether a test signing cert or the official signing cert was used. The build step somehow failed and left the strong name of the assembly invalid. So, the first part of the message in the exception was pretty acurate. It just did not tell me which assembly could not be loaded. Nor was FUSLOGVW.EXE any helpful here.