I am running Office 2007 and just had the same experience. I was renaming some portraits I'd taken of my son. I selected all the photos in the folder (54 of them), and used the rename feature, asking the software to number sequentially. It numbered them sequentially, but pictures 10-20 are missing. I have been unable to find them anywhere on my hard drive.

I have already run one file recovery software with no luck and am getting ready to try another that is more in-depth. I would love to know if anyone else has had this problem and if it can be fixed.