It sounds like you have the type of 4th axis that requires a brake when in position, the other style is that there is no brake and the servo hold position, these latter types are usually capable of interpolated motion with the other axis.
In your case you need to disable the drive when in position at the time the brake is applied.
IOW, you should never keep the motor engaged or active when the brake is on.
If the Granite drive has a In-Position signal which is only on when the motor is stationary, you could maybe read this signal and then in turn issue an output that turns the drive enable off, this would be OK as long as the motor remains in position however.
This may require some simple logic, either in the controller or external.
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.