Two possible reasons, if they are large AVIs, it may take longer to create a
thumbnail. Or, the could be DivX AVI files and the codec is not loaded (but
if you played them, that would not be true.) Does waiting in the directory
make a difference? Also, on the tools, options for the explorer window,
view, is Do not cache thumbnails checked?
Recieved another response that really did the trick check this link if you are interested
http://windowsxp.mvps.org/videothumb.htm