Editing Wordpress category gives PHP line/parse error

Not sure when this occurred but when editing a category, this error is given at the top of the edit category page.

Warning: call_user_func_array() expects parameter 1 to be a valid callback, function 'my_category_custom_fields' not found or invalid function name in /home2/sirenon2/public_html/wp-includes/plugin.php on line 525

Line 525 is call_user_func_array($the_['function'], array_slice($args, 0, (int) $the_['accepted_args']));

When I submit on the edit category page, it gives me the original error plus:

Warning: Cannot modify header information - headers already sent by (output started at /home2/sirenon2/public_html/wp-includes/plugin.php:525) in /home2/sirenon2/public_html/wp-includes/pluggable.php on line 1228

Line 1228 is header("Location: $location", true, $status);.

Any ideas on what the problem is and how to fix it? I do have custom fields on my edit category pages.

Thanks

via Chebli Mohamed