Issues with your system configuration have been detected
General installation instructions can be found here. For more specific hints on the existing issues please have a look at the messages below.

It looks like the directory for HTML filtering caches is not writable by the webserver. Please change the permissions of /data/mappletest/vendor/ezyang/htmlpurifier/library/HTMLPurifier/DefinitionCache/Serializer and enable the user which runs the webserver to write to this directory.