This thread was asking about about the SerialKey exchange between the launcher and the client. Since I started this thread, I've now been able to understand it.
For historical purposes:
Grace Period
The SerialKey allows 60 seconds for the exchange. That is to say, the game client (theduel.exe, gunz.exe, etc) allows a minute between starting the game and opening the client, or it will refuse to start (with error 206 - see below).
Serialkey Error Explainations
201: Clipboard cannot be opened, therefore the clipboard is already in use
202: Required clipboard format not in use, so the launcher didn't set it, therefore it didn't run.. (the most common error)
203: Unable to decrypt this serialkey (couldn't derive key) UPDATED
204: Failed to decrypt serialkey UPDATED
205: Serialkey parity/checksum mismatch
206: Serialkey has expired (the client launch has taken too long since the game was started from the launcher)
207: Launcher and client launched from different directory
208: Unknown message string (from either "I_hate_hacker", "I_love_MAIET", or "Find_Me")