Sorry I can't help you much, I would just like to add that I too experience this same behavior on occasion.
For us it seems to have started after we had been working with CS5 for quite awhile but before we moved to CS5.5.
(we have not yet upgraded to CS6)
I work at an Ad Agency and we're making Interactive PDF's with embbeded video routinely.
Once in a great while we'll come across a video file that won't play as del_76 described.
Converting to another format with Media Encoder, Xinet, QT Pro or other software usually is enough to resolve the problem.
Recently, I had a .mov file that, no matter what I did with it, it would not play in Acrobat X.
The other 10 ten video files, seeminlgy from the same source, and handled in a routine manner played just fine.
I say seemingly from the same source because how do I know what has occurred with the file in it's past?
Although a file appears to be fine as recieved, has it been converted from this to that and back again and manifests as a problem only now?
We will be testing CS6 soon and I'll try to let you know if that seems to influence this problem in any way.
