Hi Shailesh,
This error message is issued due to the reduction of the PO that the system is trying to do while posting MIGO.
It is important that you know if you are PBET or not.
You see if PBET is activated in your system in transaction SE38 -> report RFFMMONI -> Run -> Click on your update profile and you will see if PBET is marked.
You can also check if you are PBET in transaction OF39 as PBET can be active in your system either for your whole FM update profile or for individual value types.
If you are not PBET, you can use transaction FMIR to open the period for the posting.
If you are PBET and wants to post without considering PBET logic (with PBET active, all postings have to be chronological, hence a PO reduction or change cannot be done in an earlier date) you can consider transaction FMOD but only if you have just few open items to be posted and few users that would do this task. When the task is finished, remember to remove the users from FMOD otherwise everything that they will post will be in that date. FMOD should be blank in your system before all the open items were posted.
I hope this helps.
Regards, Vanessa.
