Hi HeadClot -
Can you be very specific by what you mean by Import? Typically you should not have to migrate or import anything from a Preview Version of the Engine to the full Version. You would only be asked to open a copy of your project if you are going from version 4.7 to 4.8. 4.8 Preview 4 to 4.8.1 should not trigger any warning as they are the same engine version with some bug fixes.
I can see from the project files you uploaded that there is an issue with the assets, but this is somewhat normal when you copy and paste the project files from one project to another without the Migrate feature. The Redirectors can get broken if not migrated properly from the engine.
Let us know -
Eric Ketchum