Canon MF4570DN can't print two-sided (duplex)

Hi, I have a Canon MF4570DN printer, and I believe that I had no problems printing duplex at one time, though now when I try to select "two-sided printing" that option is grayed out. I don't regularly use this feature, so I can't tie the loss of the feature to any specific event. Currently I'm using the Canon MF4500 series UFRII driver (v 2.24). I have deleted this printer from my settings several times including to enable airprinting at one point, and to upgrade the driver version. Since then, I disabled the airprinting hack. Does anyone know what could be causing this odd behavior and how to fix it? Do I need to edit some hidden plist?

Thank you for any help!