Thanks for the reply, Richard! I also had taken a look at the code in System.Xml.dll from 4.5.2 and from 4.6.1 using ILSpy, but couldn't find any significant difference. Both versions had the "XmlCharType.bin" resource embedded inside the assembly. When our addon is being loaded, it's creating a separate AppDomain to avoid any side effects the host application might have, so I have no idea what they could actually do to make our addon fail so miserably. I even looked at the assemblies loaded into our AppDomain when initializing the configuration system fails and System.Xml.dll is already loaded at the very beginning, so I really cannot see what could keep the assembly from finding its own embedded resource... To my understanding, even fiddling with CAS cannot influence access to an assembly when it's already loaded, can it?
Regards, mav -- Black holes are the places where God divided by 0...