From Convention Master Documentation
Install PkippLib for EPL Printers
If your using the EPL print method within the registration system, then you will need the PKIpp Library. This library is included with Convention Master but requires some special setup in order to operate properly and be able to print labels.
1. Move into the /var/www/printing/pkipplib/pkipplib-0.07/
2. Set up pkipplib (be sure to do this as root)
sudo python setup.py install
3. Pkipplib should now be installed.
Note: If you did not install the Python imaging library in stage 2, install it now:
sudo apt-get install python3-pil