I rebiult the database as you indicated. I found the log and searched for "error", no errors. But towards the end of the log I noticed the following:

19:03:55.1 Preparing database for new data
19:03:55.2 Writing 0 Airspace Boundaries
19:03:55.4 Writing 7864 VORs
19:03:58.0 Writing 8420 NDBs
19:03:59.8 Writing 109210 Intersections
19:04:04.1 Writing 72398 Airways
19:11:28.1 Writing 24823 Airports
19:11:29.0 Writing 30960 Runways
19:11:29.7
19:11:30.6 Writing 37034 Comm Frequencies
19:11:32.1 Writing 61787 Runways (2)
19:11:35.0 Writing 85612 Parking spaces
19:11:39.2 Writing 41294 Aprons (1)
19:11:43.2 Writing 381080 Aprons (2)
19:12:11.9 Writing 28169 Taxiways (1)
19:12:14.6 Writing 359135 Taxiways (2)
19:12:25.3 Writing 487313 Taxiways (3)
19:12:31.7 Writing 20704 Instrument Approaches (1)
19:12:32.4 Writing 56545 Instrument Approaches (2)
19:12:35.1 Writing 62212 Instrument Approaches (3)
19:12:39.3 Writing 51677 Instrument Approaches (4)
19:12:42.7 Writing 140041 Instrument Approaches (5

When the data is written there are no airspace bounderies.

I also have a laptop with FSX installed, in fact a Windows8 with the 8.1 upgrade. (Your Plan-G also functions well in this new O/S)
So I installed Plan-G and ran  the databuilder.
When it finished and I restarted your programm immediately and saw all the airspaces. The log shows 21258 airspace bounderies.

One way out for me is to include all my add-on airports on the laptop and use the .sdf file from this laptop. But I was hoping that you have an easier solution, and also a reason why the airspace bounderies are not being written.

Thanks for spending your time on me.

I changed the Ip4 network mode to Pipe and left the Server Port/Pipe box blank. Now both FSX and Prep3D can be connected locally on my FS Windows7
computer.
It remains strange that Prep3D had no problem with the original Ip4 mode.
Thanks for the help, Tim.

In View mode I have "map overlays" checked and in Map mode I have ckecked all 4 boxes: ICAO Airspace, Centre, RDPM Airspace and Special Use.
But no Airspaces will show up.
Is the data for these airspaces loaded from FSX?

Except for the absence of these airspaces I am very pleased with your programm. I like using FlightSim for travelling all over the world (virtually  of course) and your programm is the best I have come across so far, even flying IFR on IVAO, using the lower airways and not switching on an FMC. I still use the official charts, entering the waypoints myself. Works fine!! Thank you.

For testing purposes I have FSX and prep3D installed on the same computer, Windows 7 OS. Normally I run Plan-G on a secondary computer via SimConnect in a home network. This works fine, wheteher I use FSx or Prep3D I can connect without difficulty. The description for this connection in the manual is very clear!
I also have Plan-G installed on the FlightSim computer in order to build the data base.
When I try to connect FSX to this particular Plan-G, on the same computer; it will not connect! But strangely enough if I run Prep3D and push the connect icon it does connect. In both cases the SimConnect box is checked.
It is not importatnt of course, but I would like to know why.

I looked through forum topics to see if the not showing up of airspaces is a common problem. Doesn't seem so.
I have my FSX and Prep3D on the Windows7 computer and an active Plan-G on a secondary XP computer, on a home network, connected with SimConnect.
I followed Tim's suggestion and also installed Plan-G on the FS computer. Then ran the Data Builder and used the .sdf files in the data folder for the Plan-G on my XP computer.
But, on neither of the two Plan-G's I can get airspaces, although the necessary boxes are checked in the Map ribbon.
In my country settings I use Belgium and decimal point.
Can you help me?