Some Forum Members Can't see Image Attachments!?

[XSIV8]

We run an automotive enthusiast forum and we're pretty noobish at doing so. On the bright side, we're growing every day but as of a few days ago, I've recieved complaints that a few members cannot see the images that are being attached. Instead, they may see something like this: Attachment 359. They can't click on it or anything. Anyone experience this or have a solution? We don't have too many attachments and most are JPEGs numbering about 360 or so.