Comment 4 for bug 57801

I don't see any problems in the error_log.
This could be a problem with the parallel port, does the command dmesg give any errors related to lp0 after trying to print?

You could try the following basic test:
1) Create a test.pnm image with e.g. the GIMP.
2) Run the following command (as root):
$ sudo -i
# pnm2ppa -v 712 -B 2 -t 10 -b 150 -l 10 -r 10 -x 160 -y 50 -i test.pnm -o - > /dev/lp0

Does this print the image?