Guess no one has solved this?
I have encountered the same issue on iPhoto 9.5, but the oddest thing is that I'm importing photos and videos from my Lightroom library (because my wife prefers to use iPhoto), and 99% of the .mov files (iphone videos) imported fine, but those at the end of my import session failed.
Because I have a huge Lightroom library, I broke it up into iPhoto libraries by calendar year. For the year 2011, every iphone video up until Nov 6 imported fine, and then every iphone video after Nov 6 was rejected. I can play the files just fine in Quicktime, and they seem to be formatted identically to those before Nov 6, so I have no idea why they aren't being recognized properly.
My libraries are being set up on an external hard drive connected by USB to my early 2009 MBP running Mavericks. The EHD is formatted Mac OS Extended (Journaled). All of my other libraries imported without any problems, including every single iPhone video.
Given that most of my videos imported without a hitch, this doesn't seem to be related to formatting of the host drive...