From your subject description, the error is caused by ANOTHER addon, which uses an outdated version of the Simconnect, likely the original FSX RTM or the FSX SP1, while the one we require is at minimum the FSX SP2 version so, the error means that, because your sim is stuck with this outdated version, a function which was only added in the FSX SP2 version of the Simconnect library, cannot be found.
Of course, during the installation, we start the Simconnect client installer, which is located under the main P3D folder, here:
redist\Interface\FSX-SP2-XPACK\retail\lib\managed\SimConnect.msi
But, in some cases, because the way other addons are made, it's possible that, even after having installed the right version, an addon using the outdated version might be able to force the sim to be stuck with this one so, distrupting other addons (like our own bglmanx.dll) which require functions only available in the FSX-SP2 version.
You might TRY installing the SimConnect.msi from the above folder, possibly after a reboot.