Thanks for reply tharon. According to the manual this should only be an alarm (correct me if I am wrong). At the moment the PLC S7 400 is reporting an external fault every 3 to 4 hours. Below is some of log file from the CPU.
Event 117 of 120: Event ID 16# 2943
I/O access error, writing
P area, byte access, Access address: 3
FC number: 129
Module address: 84
Requested OB: I/O access error OB (OB122)
Priority class: 1
External error, Incoming event
07:17:59.727 PM 10/31/2008
Event 118 of 120: Event ID 16# 2943
I/O access error, writing
P area, byte access, Access address: 3
FC number: 129
Module address: 60
Requested OB: I/O access error OB (OB122)
Priority class: 1
External error, Incoming event
07:17:59.720 PM 10/31/2008
Event 119 of 120: Event ID 16# 2943
I/O access error, writing
P area, byte access, Access address: 3
FC number: 129
Module address: 84
Requested OB: I/O access error OB (OB122)
Priority class: 1
External error, Incoming event
07:17:59.713 PM 10/31/2008
Event 120 of 120: Event ID 16# 2943
I/O access error, writing
P area, byte access, Access address: 3
FC number: 129
Module address: 60
Requested OB: I/O access error OB (OB122)
Priority class: 1
External error, Incoming event
07:17:59.706 PM 10/31/2008
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