ok, did some troubleshooting.
Using a PTO load built on WOV, it CTD with an error in the groundobject.dll
this occurs using the germany.cat, vietnam.cat and the sf2 desert.cat same result each time.
dropped the terrain into my ETO build, using the sf2 desert.cat. works great (other than dueling Focke Wolfe's over Okinawa....)
just for grins, I dropped the terrain into SF2. Also works great (defending Hiroshima with Migs was interesting....)
so it seems, in my case, something to do with the WOV build that my PTO is built on.
of note, the issue that I've had with some of the PTO terrains where the plane sinks into the runway and explodes does not show up here.