You need to provide Domain admin credentials while adding the clients for deployment.
The error message says Login Failed.
It might be a issue with the admin credentials. or firewall might be blocking.
Check these link it ll e helpful.
Preparing for client installation
http://www.symantec.com/docs/HOWTO81299
About client deployment methods
http://www.symantec.com/docs/HOWTO81302
Preparing Windows operating systems for remote deployment
http://www.symantec.com/docs/HOWTO81300