[Alan Anderson]

The Solenoid Set function's value input expects an enumerated value of Off, On, Forward, or Reverse. Those are mapped to integers 0-3, respectively. If you provide a boolean input, a single solenoid is supposed treat a false as Off and a true as On. I don't know if it would work right for a double solenoid. It's likely that you'll see the solenoid engaged as both forward and reverse at the same time, leading to an indeterminate state when the button is released.

The typical way to control a double solenoid from a button is to use a case block controlled by the button boolean value. In the true case, set the solenoid Forward, and in the false case set it Reverse. You can also use a Select (found in the Comparison subpalette) to choose between a Forward and a Reverse constant to feed to the Solenoid Set value.