I had experienced this problem a few months ago and had originally remedied it with Grognard's fix. This time however, I was unable to import my movie file taken with the iphone 4s into iTunes, even after following Grognard's recommendations. What I did do though this time was connect my USB cable directly to the iMac instead of going through a hub - Problem solved!!
Suggestion:
1. Follow Grognard's steps
Step one: turn off and on your iPhone.
Step Two : launch iTunes and iPhoto
Step three : connect the iPhone to the computer
2. Connect the USB cable directly to the computer (do not go through a hub)
3. Import movies into iphoto
4. Celebrate!!
These steps worked for me after hours of searching the boards and starting/restarting my computer as well as slinging expletives around the office like a drunken sailor!!
Good Luck!!