What does "stopped working" mean?
Did the star next to your name disappear? What about all the special registered feature? Does the splash-screen appear when starting the game?
Check the location in the registry: "HKEY_CURRENT_USER\Software\Soldat"
There should be a string-value of the type "REG_SZ" with the name "Key" and your key as data (compare to the attachment - german version). If not, add it.