Operation & & does not exist or does not include any services

What causes this issue?

You wisht to adopt services from an existing network.
To do this, you have to enter both the number of the network and the
number of the operation.
The specified operation either does not exist or does not contain any
services.

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?

Enter a valid operation.

Error message extract from SAP system. Copyright SAP SE.