H-500/50 Z Axis Issue - Alarm 56 - S03 NR 0055

Hello all,

I am getting an intermittent alarm on the Z access. 56ZEMERGENCY STOP (EXTERNAL) and PLC-I/F show S03 Servo Alarm:NR 0055 Z. I cannot find this specific error anywhere. Can someone please shed some light on this error?

Thanks!