PHP error: Cannot modify header information – headers already sent [duplicate]

Solution 1:

You cannot use header() once text has been output to the browser. As your header.php include presumably outputs HTML, header() cannot be used.

You can solve this in a couple ways:

• Move the if statement above the header include (this won't work, as you've indicated in comments that header.php sets the uid session and other vital stuff).
• Call ob_start() at the top of the script to buffer the output.

Solution 2:

If the header.php file "has the banner", then it is presumably outputting some HTML content to the page.

You can't issue HTTP headers after you have outputted content.

Solution 3:

You cannot send any headers after sending any other content. A very likely culprit is extra whitespace after your closing ?> tag in your header.php. It's generally a good practice to omit the closing tag entirely in any script-only php files.

Your error should tell you exactly what line (and what file) is sending the output.