Well, I figured out what was causing this. I'm using a tool called Scenery Config Editor to manage sceneries, ie. turn them on and off depending on where I'm flying. Turns out this tool writes entries such as these:

Active=True
Required=False

Whereas Plan-G appears to require the Boolean values in upper case, ie.:

Active=TRUE
Required=FALSE

Once I converted the case for all these values the database was created without further problems.

I'm pretty sure it can find scenery.cfg, otherwise it wouldn't show any airports? However it does show all the add-ons. This is the database build options dialog:

Hi Tim,

I've been using Plan-G for a couple of months now (3.1.2.101 currently) ... beautiful work!

Anyway, I recently added a few more ORBX add-ons and soon thereafter noticed that some of the default airports aren't showing up in Plan-G. After several database rebuilds and redoing scenery.cfg I'm still at a loss. My scenery.cfg has 286 entries, and looking at the Plan-G log I can't see any errors, but have found one odd thing, eg:

18:18:13.2 Scanning folder 126: ORBX\FTX_OLC\OLC_AA
18:18:13.2 Scanning folder 124: Scenery\Cities\FortRucker
18:18:13.2 Scanning folder 123: Scenery\Cities\KLFI_Langley_AFB
18:18:13.2 Scanning folder 122: Scenery\Cities\KORL_OrlandoExecutive
18:18:13.2 Scanning folder 121: Scenery\Cities\Eglin
18:18:13.2 Scanning folder 113: Scenery\Cities\LasVegas
18:18:13.2 Scanning folder 112: Scenery\Cities\Rio
18:18:13.2 Scanning folder 111: Scenery\Cities\StMaarten
18:18:13.2 Scanning folder 110: Scenery\Cities\Oshkosh
18:18:13.2 Scanning folder 109: Scenery\SAME
18:18:13.2 Scanning folder 108: Scenery\OCEN
18:18:13.2 Scanning folder 107: Scenery\NAMW
18:18:13.2 Scanning folder 106: Scenery\NAME
18:18:13.2 Scanning folder 105: Scenery\NAMC
18:18:13.2 Scanning folder 104: Scenery\EURW
18:18:13.2 Scanning folder 103: Scenery\EURE
18:18:13.2 Scanning folder 102: Scenery\AUST
18:18:13.2 Scanning folder 101: Scenery\ASIA
18:18:13.2 Scanning folder 100: Scenery\AFRI
18:18:13.2 Preparing database for new data
18:18:13.3 Writing 0 Airspace Boundaries
18:18:13.3 Writing 607 VORs
18:18:13.4 Writing 547 NDBs
18:18:13.4 Writing 8990 Intersections

It looks as if the process stops scanning folders after 100. Folder 99 is the first of the base scenery folders, Scenery\1107. I've added and removed scenery entries to see if it makes a difference, but it always gets as far as the base folders. Also, that 1107 folder looks normal to me, and certainly the base airports are showing up in P3D.

Any ideas what might be going on?

Thanks
Gunther