See long text for reasons for lock indicator

What causes this issue?

There may be several reasons that lock indicators appear in the first
column. For example:
The master inspection characteristic is unlocked and only used as a
copy model.
The characteristic is not completely maintained.
A user exit is active (see Implementation Guide).

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?

Error message extract from SAP system. Copyright SAP SE.