& not identified as a global object

What causes this issue?

An attept was made to generate an interface for a global object which
is not contained in the list of global objects.

System Response

Generation of the interface is terminated.

How to fix this error?

Maintain the list of global objects in the global object tree. The
transaction 'SMOG' is used here. You can activate generation of the
interface from here.

Error message extract from SAP system. Copyright SAP SE.