Error – gzip??

Warning: ob_start(): output handler ‘ob_gzhandler’ cannot be used after ‘URL-Rewriter’ in /home/xyz/public_html/wordpress/wp-includes/functions.php on line 829

Hi,

I get – today – the above error on a site after activating gzip (that was the last action while working on it). Dunno though whether it has anything to do with this at all, as yesterday there wasn’t any such error.

It is shown onscreen during the first load, on reload it vanishes.

Any ideas?