You don't mention the brand of memory card or if you formatted it in-camera before use. Both can be important factors. Some cards are better than others... and some brands are frequently counterfeited. Regular in-camera formatting is a good idea.... just to be certain the card is set up properly for the camera.
You also didn't tell us your method of download. That also can be important. Downloading via USB cable is not as reliable as removing the card from the camera and downloading images via a card reader.
Is the card new, or has it been used for a while? Has anyone else used it in another camera?
Also, any changes to your computer or card reader?
If your other cards are working fine without any issues, it's most likely that particular card... not the camera.
If you're seeing this happening on multiple cards, there's greater possibility it's an issue with the camera (or your download procedure). If it seems to be the camera, first thing I'd do is try a firmware update (or reinstall, if it's already up to date). That can solve problems, is relatively quick and easy, costs nothing to try and if it works will save having to be without the camera while it's out being checked for issues.
There have only been two times I've ever had corrupted images from memory cards... and both were my own fault
- Once was when I interrupted the camera while it was still writing to the card (an older camera that was slower writing images). I opened the memory card door before it had completed writing.... I was able to recover about 3/4 of the images from that card.
- The other time was a connectivity issue. I'd added a USB hub to my computer to accommodate some added devices and was running a card reader through that hub. I saw a number of images corrupted. As soon as I switched it back and directly connected the card reader to one of the computer's USB ports, all was fine again. I didn't lose any images because I never "move" images from my cards... I always "copy" them instead (leaving them on the card until I know for certain the copies are safe and secure on the computer).
Other card issues I've had over the years (without any corrupted images):
- I also had trouble with one or two cards that I'd lent to a friend, who used it in another brand camera. First time I tried to use them in my cameras, they wouldn't work correctly. I caught that before taking any images and after formatting the cards again worked fine in my camera. (Note: I have never had any problem using cards in different Canon models that I use, though I make a habit to format every card before use... and that might have something to do with it.)
- Out of probably 100 or more memory cards of various types I've used over the years, I've only had two cards fail. One was a brand new SDHC that the camera and computer wouldn't even recognize, right out of the package. Couldn't use it at all. The second instance was a new Compact Flash card that worked once, then seemed to lock up after partial download of the images. We were shooting RAW + JPEG and had downloaded only the JPEGs on location... That went fine. But later on when I tried to download the rest of the images, the card was unreadable and inaccessible (both on my desktop and on the laptop we'd used earlier to download the JPEG versions of the images). Both instances the cards were a top brand name, high performance and high quality. Neither appeared to be a counterfeit, either.