Hey, I'm brand new to the fourum. Last night I just purchased Fly Inside for FSX. I had tried the trail for the 15 minute runs like 3 times and I was sold. However, I seem to be running into extremely similar situations as the OP and the co-OP (lol, not sure if that is even a thing, but Dan had the two of them email him.) When I was reading this, I realized that I was experiencing the interact button issue too, but I also have a few more symptoms to point out:
When moving windows around in the cockpit is usually always where I get a crash. Interacting in the cockpit is far less likely to crash it and using the mouse to interact essentially avoids the issue. But the moment you interact with a popup window, you've sealed your fate. It is a matter of when it will crash. To speed up the crash process, try resizing or moving the window and you are guaranteed a crash within the next few seconds.
I know this post is old, but the symptoms are so similar and I didn't see another fix except the "make sure fsx is on the foreground." However, this doesn't resolve the issue that I'm having by moving the windows around or resizing them.
Thanks for the help in advanced!