I need to import Robohelp projects with *.xpj names into Robohelp 2019 Classic. but it only wants to see *.hpj names. Rename the extensions?
IIRC there's an Import old projects route - how are you trying to access them?
I'm thinking this should be as simple as just opening 2019 Classic, then using the option to navigate to the 2011 project and open it up.
Got it imported through its hhp file, that was then upgraded to 2019. Compiled correctly.