Movies not playing in iTunes 10.5.3

In the past few days I have downloaded some movies through iTunes, some through iTunes purchases and some by entering the digital copy codes that came with DVDs/Blu-rays. When I try to sync these items with my iPad, I get a message that they cannot be synced. When I try to create an iPad version through the advanced menu, I get a message that they cannot be found. When I try to watch them on my MacBook using iTunes, I get a message that the movie requires QuickTime, which is not compatible with this version of iTunes.

How can I get these items to play and sync? They work if I open iTunes in 32-bit mode, but this is an annoying workaround. Plus, the iTunes support article says this is only necessary for "older media files" -- these are not old media; I just downloaded them. What is Apple doing selling files that are incompatible with its current version of iTunes? If I had known I had to go through such trouble to get them to play, I probably would not have bought them in the first place.