It’s a strange message (the type was never defined in an assembly with that name, and how does the project remember the old version?)
But you should check that the ExcelDna.Integration file which should be referenced from the new project exists in the right location.
The recent anti-virus confusions have sometime removed this file, leaving an unpacked NuGet package in the NuGet cache that is missing this file.
I suggest you look around, and if it looks fine, check that a new Excel-DNA project works fine.
If that works but the upgraded project is still a mess, you can post the whole build output.
We can also arrange for a paid-for support session and I can try to sort it out remotely.
If you’d like to try that you can contact me directly.
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