Multiple values indicator cannot be deleted

What causes this issue?

You want to delete the "multiple values" indicator, so that only one
value can be assigned to the characteristic.
The characteristic is already in use. The system check of the values
already assigned has found at least one case where the characteristic
has more than one value assigned to it. This means that deleting the
indicator would lead to inconsistencies.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

Reselect the field.
Before deleting the indicator again, first check all the values
assigned to the characteristic and delete the multiple values if
appropriate.
By choosing function <LS>Environment -> Where-used list</> from the
characteristics menu, you can find out where the characteristic has
been used.

Error message extract from SAP system. Copyright SAP SE.