So, this is a very stupid issue, and a really annoying one as well . But really simple to fix. These instructions are valid for apache 2.2.22, with default settings
run following command
If you see something like following
[Wed Feb 20 19:31:19 2013] [error] [client 127.0.0.1] PHP Warning: Cannot modify header information - headers already sent by (output started at /var/www/vtiger/include/utils/ListViewUtils.php:1) in /var/www/vtiger/index.php on line 91
“/var/www/vtiger/include/utils/ListViewUtils.php” could be any file path, similarly “/var/www/vtiger/index.php” could be any path as well. The key over here is the :1. That means the issue is at the line 1. This might be because of something called Byte Order Mark or BOM.
Open “/var/www/vtiger/include/utils/ListViewUtils.php” in vim
and save the file without a BOM:
:setlocal nobomb :w
To ask Vim if there is a BOM:
Simple, this should fix it.