Why can't I view photos from USB?

[bestpic]

I'm new to the forum !

I'm trying to view phtos from a USB (8 Gigs, brand new) but half of them don't appear. They are on the USB and appear as thumbnails on the screen when I insert the USB. Then, some appear whilst for about 50% of them I get an error message 'image not available'.

I though it was Picasa messing about but even when I downloaded directly from 'my pictures' I get the same problem.

Any help would be gratefully received!

[Blencogo]

Have the pictures that do not appear been edited/rotated/cropped?

Sometimes pictures edited by another program cannot be displayed.