Updating problem

I tried the automatic update, but it was an incomplete upload. I got an error message, checked the forums and tried re-naming plugins to plugins-hold while adding a blank plugin folder and reverted my theme to twentyten. Now I get this when I try the auto upload again:

Fatal error: Call to undefined function is_network_admin() in /home/blakehay/public_html/blog/wp-admin/admin-header.php on line 16

Any ideas?
I seem to only enough to get myself in trouble!
Thanks!