lost duplex ability in proprietary software program

Good Day!
Let's see if you can help with this... I'm not sure what category to post to hardware?software?, so I'll throw it here and let you guide me.
I have a HPLJ2420 printer that will no longer duplex when launched in one proprietary software program. It duplexes perfectly in other programs; has just stopped working in this one. That program was recently upgraded. This function was lost after that. The developers are telling me they can't replicate my problem at their location (they don't have my printer model). Can anyone suggest where the "bug" might be that would block this function within a program and what it might be? I have current PCL 6 driver, most recent firmware upgrade loaded. And, function works in other programs so I know it's not the printer. Just need some thoughts on where to tell the clowns who wrote the new program where they may have messed up so it can be fixed. Best Regards! -Connie

When you go to the queue properties/advanced, can you check if the duplex unit is marked as installed, sometimes it only enables manual duplexing? I think that on a duplex unit, only one of those items can be replaced at a time for it to maintain the duplex option.

This printer does not have a manufacturer installed automatic duplex; it has duplex ability via manual settings. As it is, it works fine & duplexes in all other programs. The setting you refer to is showing as "uninstalled". 'Advanced Features' = enabled. 'Allow Manual Duplex' = enabled. But, I will try to "install" it and see what happens. Thank you for pointing this element out. I will post again after my test.