Choose another object type

What causes this issue?

You have executed Goto->New relationship environment. During this your
cursor was placed on the central object type. As the relationship
environment has already been displayed for this object type the desired
function is not meaningful.

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?

If necessary position your cursor on another object type.

Error message extract from SAP system. Copyright SAP SE.