I was receiving the same error message after updating 3 of my macs to Lion. Switching to 32 bit mode made no difference whatsoever. I suspect my situation is quite different and I'll post my solution here just in case anyone else has such a wacked out installation as mine.
Here's my situation:
- 1 PowerMac G4 with 7 terrabytes of eSATA discs functioning as a file server (obviously can't be updated to Lion or even Leopard, but works fine as a file server and let's me use eSATA discs). I've ripped my entire DVD and CD collection ( _hundreds_ of DVDs CDs)
- 1 MacMini in the entertainment center which mounts a volume from the file server and which the mini uses as it's storage for iTunes. The mini is the "primary" iTunes library that the other machines access via Homesharing
- my MacBook Pro
- my daughters' iMac
- oh, also an AppleTV in the entertainment center
We used Homesharing to be able to watch movies and TV shows on the "remote" machines. After updating to Lion on the macbook pro, the iMac and the mac mini, I was getting the above error message "This movie requires Quicktime, which is not supported by this version of iTunes." Trying to play the same movies, etc, directly on the mac mini didn't generate the quicktime error, but rather, the error about not being able to find the files. After showing iTunes where the files were, the error message went away on the mini, and the "remote" machines were able once again to play the movies and TV shows without the error, even when in 64 bit mode.
I know this is a wacked installation, but other than the file server, I'm guessing lots of people have a "big" mac somewhere with all of their media that they access via homesharing, so this might help someone.