Some photos not transferred to iPhone during sync

I have just synchronised my iPhone with iTunes on a Mac and the following error message was produced:

"Some of your photos, including the photo “IMG_0076.jpg”, were not copied to the iPhone “<phone name>” because they cannot be displayed on your iPhone."

This has never happened before, so I looked up the photo in iPhoto, only to find that it had been taken with the iPhone and had happily displayed there until I deleted it after importing to iPhoto. Three or four photos had been excluded from the sync, all taken on the same day, but others taken on that day were moved across correctly.

I have no idea whether the problem lies with the phone, iPhoto, iTunes or what, so I've picked this forum as the most appropriate (I hope). There is plenty of room on the phone, everything is up to date and working fine until this issue.

iPhone 4 software version 4.3.5

iTunes 10

iPhoto 09 v 8.1.2 (424)

iMac Intel

All help greatly appreciated.