Error generating image with ghostscript

 

Error generating image with ghostscript, debugging info:

Command:

'/usr/bin/gs' -q -sDEVICE=png16m -dSAFER -dBATCH -dNOPAUSE -r'100' -dFirstPage='1' -dLastPage='1' -dDOINTERPOLATE -dGraphicsAlphaBits=4 -dTextAlphaBits=4 -sOutputFile='/var/moodledata/temp/assignfeedback_editpdf_test/image_page0.png' '/var/www/html/moodle/mod/assign/feedback/editpdf/tests/fixtures/testgs.pdf'