Okay, I have started taking a look at this mysterious d3d8thk.dll. pwet99 was kind enough to send me a package of a whole bunch of them. I also looked at the source code linked at the top of this thread.
First thing I did was ran network monitor on it. Interestingly enough, the version of d3d8thk.dll that is included with the AL 4.0 1 click start v2.1 package is talking with some IP over in Mountain View, California. The IPs it's talking with are in the 74.125.225.xxx range. (74.125.225.115, 74.125.225.78 are some of the ones I've seen). oscp.verisgn.net also came up.
I can say that this is completely unnecessary traffic, and quite suspicious, because I unplugged my network cable and tried running the client and it worked fine. As to what exactly that dll is doing to fix the 'No game server is available to the authorization server. (6)', I haven't been able to figure out yet.
However, the text of that error made me think of something that I had to do to get my L2 server up and running. There was a batch file in the loginserver for L2 that you had to run to register a game server. It displayed a list of all possible game servers, you chose an ID and it would generate a hexid.txt file that had a big Hex number in it to identify which game server the login server was connected to. That text file was then copied in to the config folder for the game server.
This seems like the same problem, and having setup both L2 and Aion now, the servers are very similar. I don't know how they got the hex list for each server in L2 or how they load it with the server. I will need to do some more digging.