Rockwell Automation 1772-LS_LSP,D17726.8.6 PROG/OPER MANUAL-MINI PLC-2/05 - Manual (Page 230)

Program Troubleshooting
Chapter 19
19-9
replace the error with its correct instruction, replace the instruction, or
remove it. The ERR message caused by an illegal opcode cannot be
removed directly. instead, remove and replace the entire rung. You should
identify and correct the cause of the problem in addition to correcting the
ERR message.
We showed you several special troubleshooting techniques you can use
during start-up and processor operation.
Chapter Summary