I have been recently coding a bit for FSX. My idea is to create a flight logger with basic information, specifically on landing data analysis, then expand on that - for fun and learning too. I say this because these names in your error message are something I've seen during this effort (pardon if you already have all this info

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SimConnect is the name of the SDK that Microsoft created so external software could communicate with the simulation. You can read values from or write values to the sim using it. Microsoft.FlightSimulator.SimConnect is the reference name used in the program source code to access the libraries that allow such information exchange.
As you are running an addon, my take is that it is trying to access the assemblies (probably dlls) that contain that SimConect library implementation, but is not being able to find them in your box.
The main dll for SimConnect is called simconnect.dll (!!). It is generally installed automatically with FSX, but it may be that you have a problem with that dll installation or some of its dependencies.
I found this URL that may be of help.
http://www.fixpcdll.com/repair-dll-exe- ... error.htmlIt has some links like "Download Microsoft.FlightSimulator.SimConnect.dll Error Fix Tool Now" which I would ignore, but it could give you some info on how to go about solving it. You can also try tools like Dependency Walker, that will build a tree representation of your dll dependencies and help you figure out what may be missing. This can get a bit technical, but dll problems are kind of pesky most of the times :S
Hope this helps!