I've had this problem too. What's happening is that one hit of the solenoid isn't enough to drop the sear. It's like a hammer taking more than one hit to drive a nail.
Remember, always store your SLG with the battery in upside-down.
That way it won't drain before your next game.
Also, if you have a Sam's card, you can get 5 Energizer alkalines for around $10, which is a lot cheaper than most stores.