PO cannot be changed accordingly to PR change due to PBET

Hi all,

PBET is activated in our development system.

I created PR in date 26.02.2014, then I created a PO with reference to PR on the 26.02.2014.

On 27.02.2014 I changed PR account assignment (WBS). The PR change is recorded as per system date 27.02.2014. Then when I try to change PO WBS accordingly to the new WBS entered in PR, the system gets the following error message:

"Posting date/period 26.02.2014/002 is earlier than existing date/period 27.02.2014/002

Ensure that the FM customizable date is not earlier than the original or change account assignment posting date.

Add/Change the FM customizable date using the following link: FM Customizing Date."

I’ve tried to populate through FMOD trx FM customizing table with date and with 27.02.2014 but the error still appeared.

As of now PO cannot be changed in any way, so the budget committed there cannot be spent neither reversed in any way.

Anyone can help me in understanding how to change PO?

Thanks a lot.

Manuela