While my problem is similar to one reported last month, there are some subtle differences and some additional information. I'm using SBuilder but, based on other threads/forums, similar problems also occur with Ground2K4. Basically, at dusk, many of my VTPs disappear and, in their place, I see the underlying landclass. The situation is the same at night. If the underlying landclass has lights, these show also. But, at dusk, all the characteristics of the underlying landclass are visible - whether or not it has lights. I have installed another addon that assigns landclass. If this addon is enabled in the Scenery Library, I see the landclass it lays down. If it is disabled, I see the default landclass. In the case of my airport poly, only parts of it disappear - on LOD13 boundaries, not on the landclass boundaries which are in the middle of the LOD quadrant. All VTPs (or parts thereof) in the problem quadrants disappear. As well, my UT Canada/Alaska roads also disappear - again at the relevant LOD boundaries. This suggests an exclusion problem, but exclusions don't apply just at night. Using LWM Viewer, I've examined every file (except exclusions) that affects the area. I was looking particularly for anything that affected only the probem quadrants. Nothing! I disabled all my exclusion files as well as the default AB, AP and FL scenery files. No change! Previous threads in this and other forums have suggested the problem is due to combining night-lighted VTPs (like cities) and non-night-lighted VTPs (like grass) in the same project. The fix seems to be to split the project up so that lighted VTPs are in one project and non-lighted ones in another. But, that's not my situation. None of my VTPs - grass, dirt, forest - have lights. However, just to be sure, I created a new project containing nothing but my airport poly. I tested three ways, i.e., the file: in the project folder, in a different folder under a separate heading in the Scenery Library, and in both. Again, no change! I've also tried all three ways to set up the VTPs. For my airport poly, I first used landclass texture 10 - Grass. I got lights all over the city-side of the airport at dusk. Then I tried the assembled texture 1183 - Grass. It solved the night lighting problem, but some of the underlying landclass "bled through" during the day. Finally, I tried a named texture set which included textures for all seasons and for night-time. The night-lights were back. I'm stumped! Any suggestions (for which I thank you in advance)? Don EDIT: I've done some further experimentation. I added a VTP textured with a cityscape, including lights. It too disappears at dusk and is replaced by the underlying landclass. As well, the "bleed through" mentioned above is present at dusk/dark as well as in the daytime. It appears that landclass takes precedence over VTPs when night texture is to be displayed.