Permalinks missing on most media

On the site http://pbmc.seas.upenn.edu/, we have a lot of graphics which have extensive captions and descriptions. I’d like to let users click on the embedded media, and bring up the Attachment Pages so they can read this material.

However, most of the media items I’ve loaded into the site don’t have working Attachment Pages. Some do, some don’t, and I don’t think I did anything different when I imported them or placed them. So I don’t think the problem is due to any plug-ins or the theme.

(For example, the link
http://pbmc.seas.upenn.edu/?attachment_id=434
works for one graphic, but the link
http://pbmc.seas.upenn.edu/?attachment_id=410
doesn’t.)

Is there a straightforward way by which I can get my site to use or create the proper Attachment Pages?