The shell command
"/l/www/moodle/filter/tex/mimetex.linux" -e "/m/floppy/avle/moodledata/filter/tex/d9b16d7e8200a876e5cc56e91090781f.gif" -- '\Large \sum_{k=0}^{n} aq^k =\frac{a(1-q^{n+1})}{1-q},'
returned status = 126
Image not found!
Please try the debugging script