It looks like the E120 without network only supports PCL6 while the E120n additionally supports PostScript but only binary via TBCP protocol (Lexmark calls this Mac only).
I have manually added "*Protocols: TBCP" line to the PPD-O-MATIC generated Lexmark E120n Foomatic/Postscript (recommended) PPD in attachment. Can you test whether you can print with this PPD? If it works we can correct it in foomatic database.
It looks like the E120 without network only supports PCL6 while the E120n additionally supports PostScript but only binary via TBCP protocol (Lexmark calls this Mac only).
I have manually added "*Protocols: TBCP" line to the PPD-O-MATIC generated Lexmark E120n Foomatic/Postscript (recommended) PPD in attachment. Can you test whether you can print with this PPD? If it works we can correct it in foomatic database.