The Z axis servo drive is not turning on for some reason. It could be a blown fuse or a tripped breaker on the drive unit itself.
When you turn on the control, it boots up, then it sends a signal to each of the servos to turn on. Each servo has to respond with a "Velocity Unit Ready" or "V_Ready" signal within about 1/10 second, or else you will get this alarm.
Focus your attention on the Z servo amplifier and see if there is anything amiss. You might be able to see a red alarm LED on the servo board.