Don't for iTunes into 32-bit mode...
Here is what I did
Using a Mac
1. Copy the movie to your desktop from iTunes
2. Delete the movie in iTunes, DON'T keep the file
3. Drag / Drop movie back into iTunes
4. Should fix it
Using an iOS Device
1. Delete the movie from iTunes
2. Download the movie again from your iOS Device
3. Sync the iOS device to iTunes
4. Transfer purchases
5. Should fix it
I have just tried what you suggested, and it works well, but then i discovered there is no need to move the files.
So skip point 1
2 Delete the movie in Itunes, BUT keep the file
3 Click File add to library and browse to your media folder where your files are downloaded from Itunes and selct the movie file.
My Library and media files are on a NAS drive and in advanced preferences I have selected not to copy files to media folder when adding to library. Hope this works for others.