Like others have said, the ATC2K uses Motion-JPEG, the amount of motion won't effect how much data is used for each frame, the complexity of the image will effect it though. If you leave the camera running, pointing at a plain wall, the data rate will be relatively low, if you point it at a complex image, it'll be high, and a slow memory card is more likely to fail if you are sending a lot of data to it. If you are testing it in the office, make sure it's pointing at something with lots of complexity, ie no big areas of blankness.
When I first used my ATC2K with a cheap card, it randomly stopped after different periods of time, and whilst the card "lost" capacity, there was generally no associated video file. I had to reformat the card to regain the capacity. I assume that when the data rate being written to the card exceeded what it could deal with, the microcontroller barfed, and fell over, and didn't close the file correctly, leaving a corrupted structure on the "disc".
When I first used my ATC2K with a cheap card, it randomly stopped after different periods of time, and whilst the card "lost" capacity, there was generally no associated video file. I had to reformat the card to regain the capacity. I assume that when the data rate being written to the card exceeded what it could deal with, the microcontroller barfed, and fell over, and didn't close the file correctly, leaving a corrupted structure on the "disc".