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Please see the official X‑Plane Support page for help.
Firstly I am not with Laminar Research.
If, as you say, are running the demo version then you are restricted to a time limit of operation (10 minutes?)
So that the experts can indicate what your problem may be is that you need to attach the Log.txt file to this question. The attachment needs to be attached immediately after X-plane crashes. The file can be found in the root directory of X-plane and can point to the problem
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