Probable cause.
I have had to enable "hotlink protection" on my domains due to unfortunately people (no - not you) linking to pictures from here and other sites in my account. What then happens is someone else sees the pictures and links to it again. Hotlink protection stops this. I wouldnt have a problem with it except I only get a certain amount of traffic per month (which these hotlinked images use up very quickly) and I'd rather it be used for you guys than someone else. (if you WANT to link to a piccy etc please email me).
If you are running anonymising software such as Norton which blocks your referrer ID my site will assume you are hotlinking and block the image. If you are one of those unable to see smilies can you try accessing the forum with the software turned off and let me know if you can then see the images. If you can then I'll know what the cause is.
Thanks.