Source system & is not an external system

What causes this issue?

Source system &V1& is not a source system in the sense of the Business
Information Warehouse.
Information on the InfoObjects in this system is automatically
requested and cannot be manually maintained.

How to fix this error?

Enter the name of an external system, or change the definition of this
InfoObject in such a way that it is recognized as belonging to a source
system.

Error message extract from SAP system. Copyright SAP SE.