Helpppppppppppppppppp

[tomorrowstreasures]

See that black box?? That is what I found when I uploaded this batch of photos. The BW photo is the same photo as the black box. I edited it in Picassa-was able to save the photo, but I am not all that pleased with the results...

I have no clue how it happened. This is what I know:
-Canon 5D digital camera, Canon 50mm EF lens
-I placed my 50mm lens on about 10 minutes prior to the shoot.
-I took the photos.
-I viewed the photos on the review screen. They were ok.
-I switched lenses
-I resumed the session.
-I downloaded the photos that night.

Any help so that I can avoid this would be greatly appreciated!