Hello Meredith,
Just so we can be sure we’re ruling out all the possibilities where problems usually occur, can you confirm that you’ve done all of the following?
1. Are you running the latest version of WordPress?
2. Are you running the latest versions of our plugins (2.0.7)?
3. Have you tried deactivating all other plugins to rule out a conflict?
4. Have you tried reverting to the Twenty Eleven theme to see if it’s something with your theme?
5. Try setting your permalinks to ‘postname’ in Settings > Permalinks?
6. Try refreshing your permalinks by visiting Settings > Permalinks (it does it automatically)?
7. Try increasing the PHP memory for your website: http://www.dailyblogging.org/wordpress/increase-wordpress-memory-limit/?
Knowing that you’ve taken all these steps will really help us source the issue you for you. It is rare that weird quirks like this are not solved by one of the above steps.
Thanks!