MSTR instruction not reading

I am reading about the MSTR instruction (Modicon Ladder Logic Block Library User Guide (840 USE 101 00))

Has anyone got an easily understood explanation of how to set up a MSTR block for the read function on Modbus plus.

We have a case at work where we use two MSTR blocks to read Information from multilin relays.

They both stopped reading last year, apparently someone toggled the success bit a few times and started them reading again??
They are both not reading again and there is no error code, any thoughts?

Sorry its been a few years and i cant remember a fix for you. MSTR and MB+ : have had some fun with that in the past!!

Re-read all the documentation you can get, and the help files - I have had to do it in breakdowns before. Its been too long sorry.