Title: [Plugin: Advanced Custom Fields] Cannot modify header information error
Last modified: August 20, 2016

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# [Plugin: Advanced Custom Fields] Cannot modify header information error

 *  Resolved [amanvirk1982](https://wordpress.org/support/users/amanvirk1982/)
 * (@amanvirk1982)
 * [13 years, 10 months ago](https://wordpress.org/support/topic/plugin-advanced-custom-fields-cannot-modify-header-information-error/)
 * Getting these errors when I click on the Custom Fields Tab in wp-admin… It happens
   only when I install multisite… But when I was working offline on my computer,
   everything was working fine.
 *     ```
       Warning: preg_match() [function.preg-match]: Unknown modifier '1' in /home/finetevj/public_html/niitpalampur.com/wp-includes/class-wp.php on line 201
   
       Warning: preg_match() [function.preg-match]: Unknown modifier '1' in /home/finetevj/public_html/niitpalampur.com/wp-includes/class-wp.php on line 202
   
       Warning: Cannot modify header information - headers already sent by (output started at /home/finetevj/public_html/niitpalampur.com/wp-includes/class-wp.php:201) in /home/finetevj/public_html/niitpalampur.com/wp-includes/option.php on line 563
   
       Warning: Cannot modify header information - headers already sent by (output started at /home/finetevj/public_html/niitpalampur.com/wp-includes/class-wp.php:201) in /home/finetevj/public_html/niitpalampur.com/wp-includes/option.php on line 564
       ```
   
 * Does anyone have a fix for this?
 * [http://wordpress.org/extend/plugins/advanced-custom-fields/](http://wordpress.org/extend/plugins/advanced-custom-fields/)

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## Tags

 * [Cannot modify header information](https://wordpress.org/support/topic-tag/cannot-modify-header-information/)
 * [preg_match](https://wordpress.org/support/topic-tag/preg_match/)

 * 0 replies
 * 1 participant
 * Last reply from: [amanvirk1982](https://wordpress.org/support/users/amanvirk1982/)
 * Last activity: [13 years, 10 months ago](https://wordpress.org/support/topic/plugin-advanced-custom-fields-cannot-modify-header-information-error/)
 * Status: resolved