Have you tried:
– deactivating all plugins to see if this resolves the problem? If this works, re-activate the plugins one by one until you find the problematic plugin(s).
– switching to the Twenty Ten theme to rule out any theme-specific problems?
– resetting the plugins folder by FTP or PhpMyAdmin? Sometimes, an apparently inactive plugin can still cause problems.
– re-uploading the wp-admin and wp-includes folders from a fresh download of WordPress?
I have had the same problem.
The reason of the problem at my blog was the plugin: “Joomla2WP”
By deactivating the plugin the problem was solved
Yes, it seems to be the Joomla2WP plugin. I’ve emailed the plugin author, perhaps he’ll fix it in a future release…