Session Write Error when visiting profile pages

I have a live site running Joomla 1.5.23, CB 1.7 and CBSubs 1.2.2

Starting this morning, our site visitors are seeing "Session Write Error!" when visiting CB profiles. These are the only pages in the site affected. I am not using the CB Facebook Connect plugin.

Live site:
www.avonlocalschools.org

On main menu, select STAFF, then any building. Clicking on any profile will throw the error.

Can someone please, please, please leek into this for me ASAP?

Rick

Thanks to an old post by krileon, I discovered that the issue seems to be with the cb_captcha plugin. I was running version 2.3 of the plugin. Perhaps I need an updated version?