couchbase-cli - not able to add server

I am trying to add a server using couchbase-cli. Command :

./couchbase-cli server-add -c caper-002.hq.northscale.net:8091 --server-add=caper-004.hq.northscale.net:8091 -u Administrator -p password

and getting the following error :

ERROR: unable to server-add caper-004.hq.northscale.net:8091 (400) Bad Request
[u'Prepare join failed. Authentication failed. Verify username and password. Got HTTP status 401 from REST call post to http://caper-004.hq.northscale.net:8091/engageCluster2. Body was: []']
ERROR: command: server-add: caper-002.hq.northscale.net:8091, 2

Tried using IP address instead of hostname :

./couchbase-cli server-add -c caper-002.hq.northscale.net:8091 --server-add=10.3.3.96:8091 -u Administrator -p password

but getting the same error:

ERROR: unable to server-add 10.3.3.96:8091 (400) Bad Request
[u'Prepare join failed. Authentication failed. Verify username and password. Got HTTP status 401 from REST call post to http://10.3.3.96:8091/engageCluster2. Body was: []']
ERROR: command: server-add: 10.3.3.100:8091, 2

Build used : 2.0.2-769-rel