SRM PO Creation with External Number Range

Hi Experts,

We are on SRM 7.0 Extended Classic Scenario and not been able to create a PO with external number and when tried received error message as "Object or set with GUID 00000000000000000000000000000000 does not exist" ,thus request to please let me now how to resolve this issue. When logged oss message the response says as per standard this is not allowed.

Thanks and Regards,

Venkata Koppisetti.