Error pdf creation

I always get an error when the cupon should be created I guess

Fatal error: Uncaught exception ‘DOMPDF_Exception’ with message ‘No block-level parent found. Not good.’ in /home/unfriedg/www/runningdinner.wien/wp-content/plugins/woocommerce-gift-coupon/lib/dompdf/include/inline_positioner.cls.php:38 Stack trace: #0 /home/unfriedg/www/runningdinner.wien/wp-content/plugins/woocommerce-gift-coupon/lib/dompdf/include/frame_decorator.cls.php(546): Inline_Positioner->position() #1 /home/unfriedg/www/runningdinner.wien/wp-content/plugins/woocommerce-gift-coupon/lib/dompdf/include/text_frame_reflower.cls.php(331): Frame_Decorator->position() #2 /home/unfriedg/www/runningdinner.wien/wp-content/plugins/woocommerce-gift-coupon/lib/dompdf/include/frame_decorator.cls.php(556): Text_Frame_Reflower->reflow(NULL) #3 /home/unfriedg/www/runningdinner.wien/wp-content/plugins/woocommerce-gift-coupon/lib/dompdf/include/page_frame_reflower.cls.php(138): Frame_Decorator->reflow() #4 /home/unfriedg/www/runningdinner.wien/wp-content/plugins/woocommerce-gift-coupon/lib/dompdf/include/frame_decorator.cls.php(5 in /home/unfriedg/www/runningdinner.wien/wp-content/plugins/woocommerce-gift-coupon/lib/dompdf/include/inline_positioner.cls.php on line 38