Inconsistent change to allowed values

What causes this issue?

You have changed the allowed values.
The characteristic has already been used. The system check of the
values already assigned has found at least one case where the
characteristic has been assigned a value that is no longer within the
range of allowed values.

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?

Undo your change.
Before you change the allowed values, first check all values assigned
to the characteristic and delete or change the values that do not
correspond to the allowed values you want to change to.
To see a list of where the characteristic has been used, choose
<LS>Environment -> Where-used list</> from the characteristics menu.

Error message extract from SAP system. Copyright SAP SE.