Projection views may not contain more than one table

What causes this issue?

Projection views are used to mask fields out of a table. A
projection view may therefore contain only one primary table.

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?

Change the view type or remove the secondary tables.

Error message extract from SAP system. Copyright SAP SE.