[?]: CPU Siemens IM151-7 Stop Due to IO Error

[Johnny_7777]

Dears,
in a existing plant, a Siemens CPU IM151-7 always going to stop mode with SF red Led on, In diagnostic buffer:

Stop due to IO Error
No Relevance for user(Z2):0050(Z3):4555
Pervious operating mode: STOP internal
Request Operating mode: STOP Internal
External error, Incoming Event

Please Help
thanks in advance