The thing I loved about Mac when I first switched ten years ago is that, unlike Windows, error messages are much more specific.
This is a great example. "Your selection contians more than one kind of media."
You may be absolutely certain that your "movies" are all the same type of file, but if they were, you wouldn't see this message. There are probably a mix of MP4, MPEG, MPG amd MOV files as well as others, and that's what causes the popup.
You need to be sure you're editing the same file type, to avoid this.
It Doesn't make any difference if the file type is different! I use to do it, and now I can't. That's APPLE's Fault! They just make it more difficult every time they decide to update anything here lately! Before iTunes 11.1 I could select every movie in my movie list and Get Info, then change them all from Movie to TV Show if I wanted. Now I can hardly even change two at a time, and even if I select two movies that I bought from iTunes that are the same in every way, I still get the error message. Well I guess "He who has the money(Apple)Makes the rules". It's a shame. I will be glad when someone finds a terminal fix.
Neainc1 is on the money. I totally agree. McBlob, the file types are the same and even if they are not, I should be able to multi select them just as I always could before!
I actually called Apple Support and after a long time while the agent checked with senior tech, they agreed it was a flaw and hoped it would be fixed in an update and encouraged me to send feedback to Apple, which I did, but I'm always suspicious about it meaning anything. Still, hopefully they will fix it, but in the mean time, it is possible to downgrade to 10.7 here: http://support.apple.com/kb/DL1576