Get variable from custom game state but compile failed

I’ve defined a custom game state class named “CustomGameState”, set a variable named “gLaunchSpeed” in it and exposed on spawn. When I tried to get this variable from another class, compile error happened:

Error This blueprint (self) is not a
CustomGameStat_C, therefore ’ Target ’
must have a connection. Error Variable
node Get gLaunchSpeed uses an
invalid target. It may depend on a
node that is not connected to the
execution chain, and got purged.

What’s wrong?