I made absolutely 100% sure, the digital signatures were correct!
It was only by doing that, I could transfer the files.
The videos you are importing may be missing signatures, if that's the case add / ammend the details yourself;
ie: Date, Name, Contributing artist, Copyright should be set already, but things like that.
It was the ONLY way I could get them to import, if any field was blank - it wouldn't do it...( seems like a permissions error / fault within iTunes when importing, if there's any missing = no go )
Good luck! Let me know if it works