Indicator for SU management cannot be changed

What causes this issue?

While you were switching on/off the SU Management function, the system
found that there are still <GL:quant>quants</> in the
<GL:storage_type>storage type</> "&V1&". For technical reasons,
changing this indicator is only allowed if there are no more quants
left in the storage type concerned.

How to fix this error?

If you want to switch on/off the SU Management function, storage type "
&V1&" must first be cleared, that is, no quants may be left in the
storage type.

Error message extract from SAP system. Copyright SAP SE.