I am getting the following error when i tried to upload a video with test user account

Fatal error: Directory /home/x7visnet/public_html/include/htmlpurifier/HTMLPurifier/DefinitionCache/Serializer/HTML not writable, please chmod to 777 in /home/x7visnet/public_html/include/htmlpurifier/HTMLPurifier/DefinitionCache/Serializer.php on line 160