Seems like at least one of these constructors has a problem:
Code:
public static Drivetrain drivetrain = new Drivetrain();
public static Shooter shooter = new Shooter();
public static DigitalSystem digitalsystem = new DigitalSystem();
Without seeing your code, I'm guessing you're trying to use the same CAN ID, PWM port, or digital I/O pin for multiple components.
It's also a
very bad idea to have a variable be "public static" and not final because something else can overwrite it accidentally. You're doing the same thing in robotInit(), which will almost certainly crash your robot program with the same error that's causing this one.
If you haven't done much programming already, you should look into using RobotBuilder. It'll generate all this code for you so you don't have to worry about it.