unable to copy jpegs to memory card

Upgrade to vista about 4 months ago.previously saved JPEGS to memory stick
without problem.
Now when I copy (or move) the files over they no longer open in Window
Gallery (error message says file format is not supported or not latest
version of WG).
Looks as if when tf'ing the files the Dimension property is lost - but i've
been unable to see how/why this happens or how to fix.
Earlier images on memory card still open Ok - problem seems to relate to new
post upgrage images. have loaded latest Vista codec for my camera (Canon
PowershotS50)
Any ideas on what the problem is and how to fix ?