cannot add header

why am i getting this error??

PHP Code:

Warning: Cannot add header information - headers already sent by (output started at c:/inetpub/wwwroot/vbulletin2.2.5/progress.php:1) in c:\inetpub\wwwroot\vbulletin2.2.5\admin\functions.php on line 1617 

my first line is

PHP Code:

require ("./global.php"); 

pls help.

[Admin]

Make sure you have no white spaces or new lines before <?php.