The reason is usually that the Orbx version of the lclookup.bgl file has been replaced with another one, usually the default version.
The second reason is also that the Orbx edits to the terrain.cfg file has been replaced, once again usually by the default version.
Both these files are crucial to the correct display of Orbx Global base and all the open LC products.
It is important to be aware that if the Delete Generated Files batch file in the P3D root folder has been run, the terrain.cfg file will have been restored to its default state. Similarly, if an update to the P3D version or even a re-installation of the existing version has been carried out, the lclookup.bgl file will also have been returned to its default state.
These are not the only causes of this problem, but they are the main ones. If your scenery starts to look like this:
First, run Verify files for Global Base and for all your open LC products and the Orbx Libraries to rule out the possibility of missing files.
If this does not work:
1a. If your Orbx Libraries are installed into the P3D folder
Please try renaming Scenery\BASE\Scenery\lclookup.bgl to lclookup.bgl .off
Run Verify files for the Orbx Libraries which will replace the lclookup.bgl file.
1b. If your Orbx Libraries are installed into an Orbx Central Library, please do not rename Scenery\BASE\Scenery\lclookup.bgl to lclookup.bgl.off
2. Rename C:\ProgramData\Lockheed Martin\Prepar3D v4\terrain.cfg to terrain.cfg.off
3. Run P3D v4 once to create a new terrain.cfg file and close it.
4. Then run Sync Simulator in Orbx Central which will write back the Orbx entries.
Orbx Central\Help\Sync Simulator
5. Then try P3D again.
1. that each of these steps must be taken in this exact order or further problems will result.
2. that the term "Orbx Libraries" refers specifically to the Orbx Libraries product, it does not
mean Orbx products in general.