Edit 2:
If you are having this same problem, these steps should solve it for you.
Here is just a little more information on my experience using RedKite's fix.
Edit:
As of today I haven't heard anything from support for a week. Reading about some people going months with unresolved issues is making me nervous. My ticket number is 23810 btw. I hope something is being done about this, looking through the forums I see I am not the only one having this problem so I am assuming this is not just going to get swept under the rug.
Original:
Ok, I am having trouble with my activation for A-10C.
I have downloaded DCS World 1.2.4 (5.73 Gb). (Also from inside DCSW I downloaded the Su-25T training missions)
I then downloaded the A-10C Warthog 1.2.4 module from the website (1.05 Gb).
I then purchased A-10C from Steam. I didn't download it on Steam but instead immediately copied the CD-Key and launched DCS World.
I then went to module manager, and clicked on install for the A-10C and it then downloaded 2 updates, one that was I think 1.6 Mb, and the other was around 320 Mb.
Now when I click on training, or any of the A-10C missions it brings up the activation box. When I paste the CD-Key into the box it says its an invalid serial number, and when I click on the link at the bottom of the text box that says, I already have an Activation Key it tells me to enter a valid serial number.
Where do I find the serial number from the Steam version, as it is obviously not the same thing as the CD-Key. Please help.
Also, do I need that 1.05 Gb A-10C file, or was that 320Mb update actually the A-10C module for DCSW?
Thank you!