Unserialize error after saving Contact form settings.

I have gotten this error twice today, and I finally was smart enough to track down where it occurs.

I am able to add the contact form without a problem. After adding the form, my layout is still intact. However, after I added the data for the settings, I get the following error:

Notice: unserialize() [function.unserialize]: Error at offset 14 of 15 bytes in /Users/mchiu/Sites/drupal/includes/bootstrap.inc on line 390

After this error pops up, my site dies. My layout information is gone, and the only thing that shows up on the page is the $content information. I did a mysqldump of the database before and after the error, and a diff on the dumps shows a lot of differences in the various cache, variable and watchdog tables.

I am running php 5, drupal 5.2, Apache 1.3.3 on a Mac laptop.