ciao...ho provato a compilare il tuo codice, dopo aver installato le librerie, e non ho errori.
ti conviene controllare la libreria AccelStepper (che ha sia AccelStepper.h e .cpp sia MultiStepper.h e .cpp).
DRIVER è parte di AccelStepper.h:
class AccelStepper
{
public:
/// \brief Symbolic names for number of pins.
/// Use this in the pins argument the AccelStepper constructor to
/// provide a symbolic name for the number of pins
/// to use.
typedef enum
{
FUNCTION = 0, ///< Use the functional interface, implementing your own driver functions (internal use only)
DRIVER = 1, ///< Stepper Driver, 2 driver pins required
FULL2WIRE = 2, ///< 2 wire stepper, 2 motor pins required
FULL3WIRE = 3, ///< 3 wire stepper, such as HDD spindle, 3 motor pins required
FULL4WIRE = 4, ///< 4 wire full stepper, 4 motor pins required
HALF3WIRE = 6, ///< 3 wire half stepper, such as HDD spindle, 3 motor pins required
HALF4WIRE = 8 ///< 4 wire half stepper, 4 motor pins required
} MotorInterfaceType;