This is way out there on a limb, but one of the effects Carenado said might happen if you disabled their weather radar was missing textures like this in the VC. I wonder if there's some chance that the weather radar didn't get installed properly or validated on your system? Like I said, this is probably barking up the wrong tree, but you might check to see if the Wx radar has a "trusted" entry in your FSX.cfg.
I think you may be on the right track. I just purchased the plane today and when I was validating all the gauge files it seemed like ther was an unusually long delay and then FSX went back to the "free flight" first page and I had to re-select the Caravan. After that it seemed to load OK and it looked great from both outside and inside views. I took off and climbed out and set the auto pilot so I could "explore" the cabin. I turned on the GPS and the WX radar and all seemed fine.....until I went to the external view....almost half of the external textures were invisible. Went back inside and all the internal textures were fine. I shut down FSX and restarted and since then, about 2hrs of flying, everything is just fine. Weird, but maybe this will help track it down.
Steve
birthday2