Class "&" is locked

What causes this issue?

The class you entered is part of a class hierarchy or network. The
superior class &v1& is currently locked.
This means that it is not possible to assign values to characteristics.
You can display values already assigned, but changes are not allowed.
This has to be the case to avoid inconsistencies in the hierarchy or
network.

System Response

How to fix this error?

Wait until your colleague has finished working with this branch of the
hierarchy.

Error message extract from SAP system. Copyright SAP SE.