Title: PHP Error activating Plugin (require_once failed)
Last modified: August 22, 2016

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# PHP Error activating Plugin (require_once failed)

 *  Resolved [francois09](https://wordpress.org/support/users/francois09/)
 * (@francois09)
 * [11 years, 3 months ago](https://wordpress.org/support/topic/php-error-activating-plugin-require_once-failed/)
 * Hi,
 * Using WP 3.6.1 (stable Debian package), I got an error activating the plugin.
   The path for the files is incorrect.
 * To correct the issue, I have modified _contact-form-maker.php_ the following 
   way:
 * The first two lines of code are now:
 *     ```
       define('WD_FMC_DIR', /* WP_PLUGIN_DIR .*/ "/" . plugin_basename(dirname(__FILE__)));
       define('WD_FMC_URL', plugins_url(basename(plugin_basename(dirname(__FILE__)))));
       ```
   
 * and it works great.
 * Please tell me if it’s a version mismatch error or my installation having a problem.
 * Thanks in advance.
 * [https://wordpress.org/plugins/contact-form-maker/](https://wordpress.org/plugins/contact-form-maker/)

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

 *  Plugin Contributor [webdorado](https://wordpress.org/support/users/webdorado/)
 * (@webdorado)
 * [11 years, 3 months ago](https://wordpress.org/support/topic/php-error-activating-plugin-require_once-failed/#post-5805325)
 * Dear user,
 * The issue is caused by the WordPress version. The WP_PLUGIN_DR is not defined
   in your WordPress.
 *  Thread Starter [francois09](https://wordpress.org/support/users/francois09/)
 * (@francois09)
 * [11 years, 3 months ago](https://wordpress.org/support/topic/php-error-activating-plugin-require_once-failed/#post-5805345)
 * Hi,
 * If the WP_PLUGIN_DIR was not defined, removing it won’t change anything IMHO …
 * And on the second line, no reference exist on this define…
 * On another hand, you specify the plugins is compatible from 3.0 to 4.1.1 versions
   of WordPress, no?
 *  Thread Starter [francois09](https://wordpress.org/support/users/francois09/)
 * (@francois09)
 * [11 years, 3 months ago](https://wordpress.org/support/topic/php-error-activating-plugin-require_once-failed/#post-5805347)
 * Hi,
 * Searching the real reason, I’ve found this ticket: [https://core.trac.wordpress.org/ticket/16953](https://core.trac.wordpress.org/ticket/16953)
 * Using Debian version with a symlink on the plugin dir may cause this issue. WP_PLUGIN_DIR!
   = realpath(WP_PLUGIN_DIR). Forcing WP_PLUGIN_DIR to the realpath on config file
   solve this problem.

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

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## Tags

 * [basename](https://wordpress.org/support/topic-tag/basename/)
 * [path](https://wordpress.org/support/topic-tag/path/)
 * [require_once](https://wordpress.org/support/topic-tag/require_once/)
 * [url](https://wordpress.org/support/topic-tag/url/)

 * 3 replies
 * 2 participants
 * Last reply from: [francois09](https://wordpress.org/support/users/francois09/)
 * Last activity: [11 years, 3 months ago](https://wordpress.org/support/topic/php-error-activating-plugin-require_once-failed/#post-5805347)
 * Status: resolved