Invalid conversion mode

What causes this issue?

An invalid conversion mode has been passed to the Quantity Conversion
Interface (QCI).

System Response

Error. Processing cannot continue.

How to fix this error?

Contact your system administrator. An internal program error has
occured.
No valid conversion mode has been passed to function module
OIB_QCI_QUANTITY_CONTROL.

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

Error message extract from SAP system. Copyright SAP SE.