Inspection lot already created from previous document

Hi,

User tries to post MIGO 01 for material with QM activated.

For earlier PO, inspection lots are created at MIGO.

For another PO, the inspection lot is not created. The materials goes to unrestricted and the status GR doc has the value 6-Insp. lot already created from previous document.

What could be the error?

Thanks,

Neelima