Warning: Cannot Modify Header Information - Headers Already Sent By Php Error

After I changed something in my .php file my whole site got an error. I changed the file back to the old one but now I get this error at the top of my page: Warning: Cannot modify

Solution 1:

How did you edit the file? I'd guess you now have a Unicode Byte Order Mark at the beginning of it. Can whatever editor you used save the file with the option "without BOM"? Most decent ones can.

The big clue here is that your error comes from line 1, and line one of your file is just:

<?php

...which is an indicator that there may be something "invisible" right at the start of the file.

Solution 2:

This error normally means you have already 'print'ed or 'echo'ed some text before php trying to write into the header info.