Well we figured it out.  We had not granted Write permission on the folder that contains the images on the IIS Server.  We copied all the images, thumbnails and all, with our code when we deployed the gallery so this didn't immediatley jump out at us as an issue.  But apparently the GalleryControl was attempting to rebulid the thumbnails, and it was failing.  What finally tipped us off is we added a new folder that didn't have any thumbnails and it wouldn't work at all.