Sales order &1 is inconsistent (Table &2)

What causes this issue?

An inconsistency in the system occurred, when an attempt was made to
create a purchase order for a third party schedule line in sales order
&v1&. An attempt was made to read Table &v2& but an error occurred.

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?

Contact your SAP administrator.

Error message extract from SAP system. Copyright SAP SE.