The DigitalIOButton class is for a button on the DriverStation (e.g. connected to the Cypress module). Are you using that? Or is your switch connected to the robot? I am assuming it's on the robot. If so, are you connected it through some digital input channel? The way to access a switch connected to a digital input channel is something like this (assuming digital input channel 1):
Code:
DigitalInput limitSwitch(1);
...
...
limitSwitch.Get();