I’m having the same issue.
[RESOLVED]
I was having the same issues after using the “automatic upgrade” plugin to download WP 2.8. The following steps resolved issue for me:
STEP 1: Back up!
STEP 2: Deleted wp-admin & wp-includes folder from root directory
STEP 3: Downloaded latest wordpress version (2.8)
STEP 4: Uploaded wp-admin & wp-includes folders to root directory
STEP 5: Everything works great!
