The issue is widely discussed. Find an article that makes sense to you from this GOOGLE.
I'm using Windows ME, and lately the thumbnails in the MY Pictures folder only show the icon for Image Preveiw instead of a miniature picture.
I can still click on the thumbnail and open the large image, but this is really time consuming and annoying.
Before this happened, I would get the "wiamgr" is undefined error message, that went away, and now this problem.