While photographing Rainbow Pools in Groveland my Canon Rebel XS went busy. I had taken 3 or 4 pictures with no problem when I tried making setting adjustments for a longer exposure. I tried to take a picture and the camera said it was busy. I've waited, taken out the battery and put it back in and hours later it is still busy. Any clues? Re format card? It's a 4 gig card with lots of space.