More than likely that is the case. There are a few ways to resolve this issue. The first (and my favorite) is to become a supporting member. This will automatically give you the ability to have ten times the space that you now have, you get a cool sticker, your user name can become blue, you'll have the ability to turn off most of the ads and you will have access to a special area for Supporting Members only.
If that didn't convince you there are a couple of more ways to resolve this. a) you can go in and delete some of your previous attachments, or b) you can start using a photo sharing site like photobucket. Just remember that if you use a ps site, once you delete the pictures from that site, the link will be lost and they will disappear from the forum as well.