Solution on Windows

In php.ini, enable the mbstring library: remove the semicolon before extension=php_mbstring.dll.

Solution on Linux

1. First, install the php-mbstring library:

   1	yum install php-mbstring

2. Then, edit the /etc/php.ini file and add the following line:

   1	extension=mbstring.so

3. Save and restart the httpd service:

   1	service httpd restart