If you are getting this message:
Warning: ini_set() [ref.outcontrol]: Cannot change zlib.output_compression - headers already sent in... /home//header.php on line 2
above your header, that means that theme you are using is trying to compress output and speed your page load speed, BUT "zlib" is not enabled by your hosting provider.
Solution: open your header file (usually header.php) and just delete following code:
If you liked this one, you can buy a beer :-)