FS9 AI Night ("_l") Textures Disappearing

Recently, my AI at night/dusk/dawn don't show in their "_l" textures. If I start the flightsim at nighttime, the "_l" textures are shown for a short period (<10 sec) and then the AI reverts to the daytime textures. All my AI aircraft switch to their daytime texture simultaneously. I don't have the faintest idea where to start looking for the problem. Any help at all will be appreciated.As well, the same AI running under FSX never (not even for the 10 seconds) show in the "_l" texture. Is that a known issue with FSX or do I have two problems.Thanks in advance,Don