Mixed mode assembly is built against version 'v2.0.50727' of the runtime and cannot be loaded in the 4.0 runtime without additional configuration information.
I got this message when I tried to start a project migrated from .NET 3.5 to .NET 4.0. I case of migration, migration wizard inserts a <startup></startup> tag into the app.config file.
Solution: insert the
attribute into the startup tag. Application should work now.
Reason: .NET 4.0 changed mixed mode assembly loading mechanisms.