Event 21 of 120: Event ID 16# 456F
STOP caused by rack failure (OB not loaded or not possible, or no FRB)
Breakpoint in user program: Cyclic program (OB1)
Priority class: 1
FC number: 5
Module address: 54
Previous
operating mode: RUN
Requested operating mode: STOP (internal)
Internal error, Incoming event
07:49:35.419 AM 10/21/2012

同样，系统也没有54这个诊断地址。