Cubase Artist to Cubase Pro file issue.

The other guitarist in my band is running Cubase Artist
We were working on a song at his house and did a project backup to USB stick, so I could take the file home.

When I opened the project in Cubase Pro, Cubase prompted for the location of four of the audio files. All four files are in the Audio directory. I pointed the dialog at the directory and the song loaded. The four audio tracks were blank.

In the Pool, they are all marked as having processing applied. All four do not have have an image in the pool.

I got the other guitarist to regenerate the backup and drop box the zip file to me.
Same issue when I pull the song into Cubase Pro. Same prompt, same missing files.

I have a work around.
I opened the track in Cubase Pro 9 then saved it under a different file name. It now opens happily in Cubase Pro

We have never had any problems before transferring files between Artist and Pro versions (other than me remembering to not use any Pro features on the songs). Obviously, I’ve also told him to do the update to the latest before our next recording session. Though I wonder if the song will open in his updated version. We shall see.