How Purch. Org 0001 is auto detetermined in PM based PR?

Hi PM Guru,

The Maintenance plan got control key PM02 to generate PR for service.

In the task list, Purch org is blank and not mandatory.

When I schedule the plan, I can not save it with the following info.telling me purch org. 0001 is not accesible for me.

I have checked the parameter in Own data where there is no default value setting there

Please kindly let me know where or how the purch. org is determined.

Thank you so much,

Sally