RPi 2B not recognizing Makerbot Replicator 2

I set up Octoprint 1.4 and GPX plugin 2.6.3 on my RPi 2B to use with my Makerbot Replicator 2. However, my RPi does not seem to recognize the printer.

The best I have is this, but I suspect that the Pi is just not registering the Replicator as a USB device. Has anyone had this problem?

Changing monitoring state from "Offline" to "Error: Connection error, see Terminal tab"
Unexpected error while connecting to serial port: AUTO IOError: 'GPX plugin not able to discover AUTO port and/or baudrate. Please choose specific values for them.' @ comm.py:_openSerial:2691 (hook GPX)
Changing monitoring state from "Offline" to "Error: Connection error, see Terminal tab"
Unexpected error while connecting to serial port: AUTO IOError: 'GPX plugin not able to discover AUTO port and/or baudrate. Please choose specific values for them.' @ comm.py:_openSerial:2691 (hook GPX)
Changing monitoring state from "Offline" to "Error: Connection error, see Terminal tab"
Unexpected error while connecting to serial port: /dev/ttyAMA0 OSError: '[Errno 13] Permission denied: '/dev/ttyAMA0'' @ comm.py:_openSerial:2691 (hook GPX)

EDIT: OctoPi version 0.17.0, OctoPrint version 1.4.0, installed this morning. I'm at a loss, because googling didn't come up with anything useful