I'm not sure what the attachment limit is on Canreef's servers, it could be you've hit the ceiling on that. I'm not sure how to delete old attachments since I've never tried it myself. I'll see what I can find out .. or if someone else knows, please chime in and let us know.
I'd suggest photobucket in this case. I use photobucket and also Shaw's photoshare for some things. The only reason threads at reefcentral don't always show the pictures because the people themselves delete their old photos rather than upgrade their account once they hit the limit, or sign up with a new account so they themselves went in and deleted the pictures.
I know Titus was trying to get the Canreef photoshare going again (MUCH bigger limit than the attachments on posts) but I have no idea where he is with that at the moment (sorry!!)..