WordPress MU

Welcome.
I use latest WordPress MU 2.7 and I have problem with modify wpmu-functions.php (UTF-8 save). When I e. g. change default category:
_('Uncategorized'), 'slug' => sanitize_title(__('Uncategorized')), 'term_group' => 0) );
to:
_('Example'), 'slug' => sanitize_title(__('Example')), 'term_group' => 0) );

I see error:

Warning: Cannot modify header information - headers already sent by (output started at /home/X/domains/DOMAIN/public_html/wp-includes/wpmu-functions.php:1) in /home/X/domains/DOMAIN/public_html/wp-login.php on line 255

Got extra space or return in the end of wpmu-functions.php?
I guess, yes :)

I don't understand. I only change 'Uncategorized' to 'Exampel' and i see a problem.

It looks like you have blank line at the start of your wp-includes/wpmu-functions.php file.

Make sure the first line only contains <?php (no spaces or blank lines).

Yes, it's blank.

Ok, Thanks. I found a solution.

Hmmm... Adamnh make sure you make notes of your changes to wpmu-functions.php as they will be lost when you upgrade.

You might want to consider using a plugin instead:
http://wpmudevorg.wordpress.com/project/new-blog-default-categories-plus-search-and-replace