Product cost collector &/& being processed by user &

What causes this issue?

DEFINE &USER& = &V3&
INCLUDE MESSAGE_ENQUEUE_USER OBJECT DOKU ID TX
The product cost collector for material &V1& in plant &V2& is currently
being processed by user &V3&.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

Select a different product cost collector, or wait until the other user
has finished processing the product cost collector for material &V1&.

Error message extract from SAP system. Copyright SAP SE.