I spent about two hours today trying to fix my PowerShot S10 so I can take a picture of my phone (don’t ask). I just kept getting the same E28 error in the viewfinder and then the lens would retract. So I reformatted the CF card and upgraded the firmware (a bit of a hair-raising experience: one false move and the camera’s toast) - still nothing. Finally, I found this thread. The upshot is, no one but Canon knows what the error is and you have to pay them £150 to tell you. Or you can bang it hard… so I did. Now fixed!