Gateway Namespace & System Alias Issue

Hello Experts,

I ran into a small issue where I was able to execute the metadata but couldn't execute the service with the collection . We are having 2 servers one for Gateway and one for ECC . In gateway, I created a 'Z' project and maintained a System Alias which points to ECC for accessing backend RFC's. So here I am getting error as "No service found for namespace /SAP/ , eventhough I use "Z" objects ". Could anyone let me know what could be the issue .

Note: In System Alias Maintenance Local Gateway & Local App are not checked.

Thanks.