UOM '&' not found in appendix table (material & plant &)

What causes this issue?

Before the system posts a material document for a Hydrocarbon Inventory
Management material, it performs the following consistency checks:
For each unit of measure in the Unit of Measure Group, a line item has
to be present in the appendix table (Table MSEGO2)
For each unit of measure in table MSEG that is not initial, a line item
has to be present in the appendix table (Table MSEGO2) and the
corresponding quantities have to be identical.

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

This way, inconsistent stock level updates can be prevented.

System Response

The system stops processing.

How to fix this error?

If the error is reproducible, contact your system administrator.

Procedure for System Administrators

The inconsitency can have several reasons, for example:
Incorrect postings from external systems using function module
MB_CREATE_GOODS_MOVEMENT
Handling errors
Application programming errors

Error message extract from SAP system. Copyright SAP SE.