Yes, the PMDG 737 BBJ variant is not internally supported in GSX. This could be noticed by the generic "Exit 2" message, which is the one of a default or unconfigured airplane.
Even if you line up everything, the most important thing to configure is the variable used to control the door's status, which on 3rd party airplanes is almost invariably a custom L: var, which requires an XML expression to be checked.
Assuming the variables are the same as the normal 737 ( at least for the doors in use ), the easiest way to "inherit" a configuration of another support airplane into a variant is as follows:
- Load up the supported version closest to the variant. I don't know how many versions of the BJJ PMDG has modeled but, I see the BBJ is based on the 737-700, BBJ2 is based on the 800 and BBJ3 is based on the 900
- Open the GSX airplane editor, and edit any parameter, even of a very small amount, like raising/lowering a door 1 cm, JUST enough to trigger the editor to save a GSX.CFG in the %APPDATA%\VIRTUALI\GSX\AIRPLANES folder
- Load the BBJ version, and do the same, so GSX will create a GSX.CFG for it as well ( you said you reset it, so I'm assuming you lost your previous modifications.
- COPY the FIRST GSX.CFG ( the one for the supported version ) over the one in the BBJ folder, overwriting the one which is already there.
- Choose "Restart Couatl" from the menu, now the BBJ should have a configuration with all the custom XML expressions taken from the standard version and doors with their custom names. You can now proceed to do any required changes, like removing doors, etc.