Base unit of measure cannot be changed since EAN already assigned

What causes this issue?

You have attempted to change the base unit of measure. This is not
allowed since an EAN has already been assigned to it.

System Response

The system cancels your change.

How to fix this error?

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.