I see the message when trying to access wp admin at localhost:

Fatal error: Call to undefined function reset_mbstring_encoding() in Z:\home\localhost\www\k-gayduk.ru\wp-includes\class-http.php on line 251

I suspected plugins, however, nothing has changed when turned all of them off.

Any thoughts?

1 Answer 1


Do a complete update of WordPress, including all the files. The function named "reset_mbstring_encoding" is in the wp-includes/functions.php file and has been since 3.7, so if you're missing it or some other file, then you need to make sure all the WordPress files are up-to-date.

  • My Wordpress is completely up-to-date. I installed the latest version two weeks ago.
    – Konstantin
    Aug 6, 2014 at 14:45
  • If you're getting this error message, then something is missing or old in your WordPress installation. The reset_mbstring_encoding is indeed a defined function, so an undefined function message tells you that it is missing. Again, do a complete update and make sure all the files are indeed correct.
    – Otto
    Aug 6, 2014 at 23:20

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