Default settings are missing in the planning variant

What causes this issue?

In planning variant &V1& for view &V2& and portfolio hierarchy &V3&,
there are no default settings for the company code (field BUKRS) and/or
the summarization rule (field VERDREGEL).
Although the simulation can still be run, the simulated transactions
cannot be saved.

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.