Image (media) upload coding error?

Whenever I click the little icon to upload a picture, I get an error message. I don’t really notice any issues with this, but it bothers me that this message is displayed. It says the following at the very top of the window that appears (everything else grays out).

call_user_func_array() [function.call-user-func-array]: First argumented is expected to be a valid callback, 'media_admin_css' was given in /mnt/w0506/d12/s06/b02ce878/www/*omitted*/*omitted*/wp-includes/plugin.php on line 311

Any idea what I should actually do at line 311?