I dont quite get what you are saying. Are you saying that all the gas escaped from your Co2 Tank?
Is there any tubing going from regulator to solenoid?
Is there any tubing going from solenoid to neddle valve?
If either of the above is true, I would say that your setup is wrong. You should not use tubing inline before the needle valve. You are asking for problems when you do this. Only run the tubing after the needle valve. This is very low pressure at this point and should not cause any problems.
Use fittings to connect all components upto the needle valve. And leak test it as Richer suggested.
BTW: How much pressure are you driving the solenoid/needle valve with? You should be pushing between 15 to 25 psi on the low side of the regulator.