Unit of measure & is still used (deletion not possible)

What causes this issue?

You have attempted to delete the unit of measure &V1& although it is
still used as an alternative unit for the material.

How to fix this error?

Make sure that you really no longer need this unit. If so, first
reset the alternative unit of measure on the corresponding data screen
and then delete the unit of measure on the units of measure screen.

Error message extract from SAP system. Copyright SAP SE.