This implies you have a concurrent limit on your account. Either try as the error message suggests using a different "position" parameter, or close the other application using your DACS login identifier.

For testing purposes you can typically use the "position" of "127.0.0.1/net" on a machine that is already running a consumer with the node IP address.

Consult your market data administration team if you need to increase the number of concurrent logins as this may incur additional data fees.