thank you again geezD
the report of damaged files was from iMovie 10 on my MacBook Pro running Yosemite.
The external drive contains projects and events that go back to a macbook using SnowLeopard.
As you know ,the drive shows up in the iMovie window. I haven't paid attention to what goes onto it except when importing movies in the past I would put them on this external drive and then I assume anything involved in editing is saved to that drive? That does seem to be the case since I was able to retrieve and play projects and files from my Mavericks iMac using iMovie 9.
The damaged file warning windows only appeared on my MacBook Pro with Yosemite while running iMovie 10.
I was not able to play any of the files from the drive.
I guess the big question is ;
As Apple upgrades it's products will they be able to read files created on older iMovie versions with older OS's?