Does a request log indicate that a set of activities contained changes for a DC yet unknown to the CBS?
The log will contain a message like "A component with this name has not yet been created or activated" for the DC in question.
You should activate the activity that contains the .dcdef file of the DC. This will create the DC in the CBS. A rebuild will be triggered automatically.
Tell the user that the "Activate" dialog box in the SAP NetWeaver Developer Studio provides an option to determine dependent activities on a component level to prevent such situations in future.
Take a look at the note