Title: Warning: Cannot modify header information
Last modified: August 21, 2016

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# Warning: Cannot modify header information

 *  Resolved [letsurf](https://wordpress.org/support/users/letsurf/)
 * (@letsurf)
 * [13 years ago](https://wordpress.org/support/topic/warning-cannot-modify-header-information-113/)
 * I have content experiments set up on one of my pages. It was working fine but
   now I’m getting a strange error when I visit the page:
 * Warning: Cannot modify header information – headers already sent by (output started
   at /home/letsurf/public_html/www.cutaplug.com/wp-content/plugins/google-content-
   experiments/class-wpe-GCE.php:96) in /home/letsurf/public_html/www.cutaplug.com/
   wp-includes/pluggable.php on line 876
 * The page is [http://www.cutaplug.com/metal-detecting-secrets](http://www.cutaplug.com/metal-detecting-secrets)
 * thanks,
 * Rusty
 * [http://wordpress.org/plugins/google-content-experiments/](http://wordpress.org/plugins/google-content-experiments/)

Viewing 3 replies - 1 through 3 (of 3 total)

 *  Plugin Author [Glenn Mulleners](https://wordpress.org/support/users/glennm/)
 * (@glennm)
 * [13 years ago](https://wordpress.org/support/topic/warning-cannot-modify-header-information-113/#post-4022167)
 * I see that the experiment is working now and I don’t get any errors, so I guess
   this issue has been resolved? Would you mind sharing the solution if you know
   what caused the error message?
 *  Thread Starter [letsurf](https://wordpress.org/support/users/letsurf/)
 * (@letsurf)
 * [13 years ago](https://wordpress.org/support/topic/warning-cannot-modify-header-information-113/#post-4022168)
 * I added ob_start(); at the beginning of the main plugin .php file. Is it OK to
   do that or will it break stuff?
 *  Plugin Author [Glenn Mulleners](https://wordpress.org/support/users/glennm/)
 * (@glennm)
 * [13 years ago](https://wordpress.org/support/topic/warning-cannot-modify-header-information-113/#post-4022169)
 * I think that should work. Also see [this topic](http://wordpress.org/support/topic/error-when-viewing-pages-with-experiment-code).

Viewing 3 replies - 1 through 3 (of 3 total)

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

 * ![](https://s.w.org/plugins/geopattern-icon/google-content-experiments_9db5c0.
   svg)
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 * 3 replies
 * 2 participants
 * Last reply from: [Glenn Mulleners](https://wordpress.org/support/users/glennm/)
 * Last activity: [13 years ago](https://wordpress.org/support/topic/warning-cannot-modify-header-information-113/#post-4022169)
 * Status: resolved