Title: Warning: Cannot modify header information
Last modified: August 20, 2016

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# Warning: Cannot modify header information

 *  [JTVaughn](https://wordpress.org/support/users/jtvaughn/)
 * (@jtvaughn)
 * [14 years, 8 months ago](https://wordpress.org/support/topic/warning-cannot-modify-header-information-75/)
 * Getting this error when trying to update pages.
 * **Warning: strtolower() expects parameter 1 to be string, array given in /home/
   mzptv/public_html/wp-includes/formatting.php on line 772**
 * Warning: Cannot modify header information – headers already sent by (output started
   at /home/mzptv/public_html/wp-includes/formatting.php:772) in /home/mzptv/public_html/
   wp-includes/pluggable.php on line 934
    - I’ve done a search
 *  and read the other support topics about “Cannot modify header information”, 
   and I’ve tried removing spaces from pluggable.php, formatting.php, header.php
   and wp-config.php, but the error remains.
 * Line 772 of formatting.php is —
 * `$key = strtolower( $key );`
 * The line in context is —
 *     ```
       function sanitize_key( $key ) {
       	$raw_key = $key;
       	$key = strtolower( $key );
       	$key = preg_replace( '/[^a-z0-9_\-]/', '', $key );
       	return apply_filters( 'sanitize_key', $key, $raw_key );
       }
       ```
   
 * Let me know if there’s any other code I can drop on paste bin to help fix this.
   I’m a PHP newb.

The topic ‘Warning: Cannot modify header information’ is closed to new replies.

## Tags

 * [formatting.php](https://wordpress.org/support/topic-tag/formatting-php/)
 * [header](https://wordpress.org/support/topic-tag/header/)
 * [pluggable.php](https://wordpress.org/support/topic-tag/pluggable-php/)
 * [strtolower](https://wordpress.org/support/topic-tag/strtolower/)

 * In: [Fixing WordPress](https://wordpress.org/support/forum/how-to-and-troubleshooting/)
 * 0 replies
 * 1 participant
 * Last reply from: [JTVaughn](https://wordpress.org/support/users/jtvaughn/)
 * Last activity: [14 years, 8 months ago](https://wordpress.org/support/topic/warning-cannot-modify-header-information-75/)
 * Status: not resolved

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