Your system is not configured to run mimeTeX. You need to download the appropriate executable for you PHP_OS platform from <a href="http://moodle.org/download/mimetex/">http://moodle.org/download/mimetex/</a>, or obtain the C source from <a href="http://www.forkosh.com/mimetex.zip"> http://www.forkosh.com/mimetex.zip</a>, compile it and put the executable into your moodle/filter/tex/ directory.