John,
Sorry my first thoughts did not help.
Further reading in the help files: In the troubleshooting section, it says that JPEG's other than Exif 2.2 and 2.21 compatible images will not display properly.
It also refers to the 10D but only to say that image "information" may not display?
The only other thing I remember reading but cannot find right now, is a reference to a low quality image being the first to be displayed, then replaced by a higher quality one. I know it said that the better quality image might take a while to appear as it depended on what resources the PC has at its disposal.
By the way, I've printed out an edited version of the DPP help files. It's 68 pages worth, but useful.
Richard