Okay. You have apparently identified the building as a library object. Once the BGL file is imported, you can scroll thru the objects with arrows on the ModelConverterX task bar. When you have selected the object, select object information from the task bar and you will see a list of textures. If a texture does not also include one with a _LM suffix, it has not night texture. In such a case that portion of an object will appear very dark at night (not necessarily black). If a night texture is included in the object and that texture is missing in the sim, much worse things often happen with the object, including during the day time.