Image upload problem not answered in sticky post

I’m using v. 2.7, with the Proximity theme. When I try to insert an image, I get this message: Warning: call_user_func_array() [function.call-user-func-array]: First argumented is expected to be a valid callback, ‘media_admin_css’ was given in /usr/home/web/users/xxxxx/html/wp27/wp-includes/plugin.php on line 339 (I replaced my user ID with xxxx.)

I can go ahead and upload from my computer, but if I click on the “from URL” tab, nothing happens. I’m not given that option. No way to paste in a URL.

I’m working with WP 2.7 from the git-go, not an upgrade. Even so, I did reinstall the content and includes folders as recommended in the sticky post. No change. The Proximity theme developer says this is a WP problem, not a theme problem. Any ideas?

My test site is at https://www.larchmontgazette.com/wp27