Change Unexpected error on Error if DMN got invalidated

If user created DMN based scenario test and used a property from it and after some time that property disappeared - then if we reopen test scenario editor we got
Error as expected see

But if user wants to edit any of the value we got
Unexpected error

Steps to reproduce

1. Import DMN Traffic Violation Rules.dmn
2. Create test scenario asset for this dmn and save
3. Go back to DMN and remove Driver Should the driver... DMN objects and save
4. Open test scenario