Units could not be found for all key figures

What causes this issue?

No unit could be found for the key figures that cannot be entered. This
is because the unit of the key figure is derived from a characteristic
value which has not been entered or because the unit field of the
reference table is blank.

System Response

The key-figure can not be edited and is not displayed. This means that
only a zero will be displayed in the corresponding fields, even if
something is in the database. A value which isn't zero can not be
interpreted in this case.

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.