After finally deciding to jump to P3D from FSX Steam some weeks ago, I bought the GSX lvl 2 expansion today (from fspilotshop.com). In the meantime, I've used GSX and the FSDT airports in P3D without problems.
Now, the Add-on manager just kicks me back to the sim when trying to activate the serial number. As soon as I click the Register serial button, the Add-on manager closes and I'm back in P3D.
Any idea how to solve this? I'm using Addon manager 4.5.0.6.