Unit of measure & is not convertible to stockkeeping unit &

What causes this issue?

An error has occurred during conversion of the quantity into the
various units of measure (<GL:stockkeeping_unit>stockkeeping
unit</>/alternative units).

System Response

The system cannot post the document.

How to fix this error?

INCLUDE NA_SYSADMIN1

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.