Problems with Canon Powershot SD550

Hi all. I have a Canon Powershot SD550 Digital Elph and have come upon a problem. A few weeks ago, it stopped being recognized in iPhoto. I was at a car show and completely filled up my 512 MB card with pictures. When I came home, iPhoto would not recognize it. If I went into Image Capture, it said there was no camera attached. I brought it over to my friend and his Mini was unable to connect to it either. His Dell gave some message about the volume being damaged. We tried plugging it into his card reader and the same thing happened. We then put my memory card into his older Canon camera and it was recognized just fine. I was able to get all the pictures off through his camera. I have reformated the card from within my camera and have reset all settings to default. I still can't get iPhoto to recognize it. Anyone have any suggestions? I got it for Christmas and it connected to my Powerbook perfectly until now.