No alternative unit of measure specified

What causes this issue?

You want the system to convert from the base unit of measure to an
alternative unit of measure for the current material. However, this
alternative unit of measure is missing.

System Response

The system cannot carry out the conversion.

How to fix this error?

This is due to a program error that should not occur. Please contact
your system(s) administrator.

Error message extract from SAP system. Copyright SAP SE.