It has been a very long time since I had to deal with problems concerning the Addon Menu. A couple days ago, I finally decided to buy Instant Scenery 3 to use with P3DV2, and FSX-SE. Although it will work, supposedly, with FSX - Steam edition, I know it will entail modifying the dll.xml file correctly. IS3 installed ok into P3DV2, but I get the popup error on start up, which I have to click "OK", and then it loads.
Ah, there's where things get difficult for me. There are two things that have plagued me with difficulties throughout my years of messing with flight simulation: 1) AI aircraft - adding, making flight plans, etc...., and 2) problems with the dll.xml entries not being correct and causing addons to be missing from the drop down menu. I was also trying to get the Armament panel added for the Razbam Corsair series, and I know the dll.xml entries have to be added for that as well..... Fun and games!
I spent a few hours, trying to get things working properly, and took a break. It is most likely a easy process for some people, but I ain't one of them!
Need to add that, prior to doing all of the above, I had installed SDK into my FSX-Steam - from my FSX Deluxe Edition & Acceleration discs. So I know that is installed.......
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