Dear friends,

WillemJakobs

Is there a way to find out which FC/DB is causing the problem?

 To add new points regarding this problem.As snapshot shows, CPU complains about reading a non-existing global DB memory  in byte #0 .It is easy if you have "Open Block" available or Module address as mentioned below.As they are not provided , you can fetch them from OB121.For limitations in production line, I suggest an off-line test in your office with S7-PLCSIM and it will imitate the same situation and you can delete OB121 there and check the exact point of  error .

Event 2 of 10:  Event ID 16# 2522
Area length error when reading
Global DB, bit access, Access address:      3
OB number:      1
Module address:      2

I hope this  helps,

Hamid Hosseini

Hello again,

For invalid values,You are right.As mentioned in online manual for OB121(attached file), valid values can not be provided for S7-300(your case).I again suggest to  test the project in off-line mode and also wait until a machine/plant down time (shut down) to remove OB121 from on-line mode and find out point(s) of error (this is the case if you can not access Open block option in buffer of CPU).

If I were in your situation, I also check off-line the program for any possible non-existing DB cell in your program.

I hope this helps,

Hamid Hosseini