You mention having viewed the Santa photos on your camera.... I assume they looked okay.
But later when you put the card into your card reader, hooked to the computer, you could not find them and may have noted some sort of error.
You didn't say how you were viewing on the computer. Was it via some software? Perhaps Canon's or another image cataloging/editing software?
Some softwares will display images in a date-specific manner, so that you might not see the latest ones in the same place as older images.
There are more basic and simple ways to view and move/copy image files. I use a PC with Windows 7 and simply use Explorer to set up a folder for images on my storage drive, then again to view, drag and drop (copy) the images from memory card to that folder.
If the images on the memory card are JPEGs, they are directly viewable in Explorer (can display as thumbnail/icons in a couple sizes). But if they are RAW files (*.CR2, which are what I usually shoot), they can be moved or copied as simply labelled files, but the images themselves cannot be pre-viewed and will not show as a thumbnail/icon in Explorer. However, for 32 bit operating systems, Canon has a free Codex that can be downloaded and installed to allow CR2 to be viewed in Explorer. For 64 bit operating systems, the Canon codex won't work but there are third party Codex that are relatively inexpensive. I use one called FastPictureViewer, that cost me $15 per computer to install, and not only translates Canon RAW files, but also RAW from every major camera manufacturer and more. It works quickly and well, allows the RAW to be displayed larger in MS Picture Viewer too.
But the codex installation and viewiing images right in Explorer is completely optional. Once downloaded, you could simply point whatever software you normally use to work with your images to the folder you've created and placed the files in.
Another thing... if viewing the memory card in Explorer as a drive with folders, be sure to check if there are multiple folders on the card. After a certain number of images Canon cameras will set a second folder (and a third, fourth, etc.). It's possible the last photos you took were put into a different folder.
And, if you have previously viewed the memory card on your computer, now are looking at it again... depending upon how you are doing so, you might need to refresh the view to update and include the new images.
If you are using a Mac, it's a whole different world and I haven't used one in a decade or so, will leave it to others to advise about them. .
Aside from software-related problems, IMO the most common source of problems is card readers themselves and especially their connecting cables. If possible, try a second one. Or, connect the camera - with the memory card reinstalled - directly to the computer via the USB cable that came with it and see if the images can be found.
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Alan Myers
San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7D(x2), 50D(x3), some other cameras, various lenses & accessories
FLICKR & PRINTROOM
