Wordpress cannot modify header information
If you get an error that looks like this:
Warning: Cannot modify header information - headers already sent by (output started at /home/.hostname/username/domain.com/wp-content/plugins/myplugin/myplugin.php:345) in /home/.hostname/username/domain.com/wp-includes/pluggable-functions.php on line 272
I feel your pain. It’s one of the more cryptic error messages I’ve run into. You need to trim the whitespace from the end of your php file. In this example, the file myplugin.php has 345 lines. Delete everything after the closing ?$gt;.