Error occured during activation (see log)

What causes this issue?

An error ocurred during activation.
The planning object structure has not been activated.

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?

For detailed information, see the corresponding log; a log is only
created if logging has been switched on. You switch on the application
log from the main screen for editing planning object structures under
Extras -> Log on/off.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.