Campaign creation using optimizer: System error while reading orders

What causes this issue?

While data was being transferred after an optimization run, the
following happened:
An error occurred while the order data was being accessed. Either no
orders could be read for an existing campaign or there is another
problem, even though the campaign was changed or created in the
optimization run.

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?

Restart the transaction.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.