failed to add node to non default group in cli

Run command to add node to group 2

2015-07-01 15:26:24 | INFO | MainProcess | test_thread | [remote_util.execute_command_raw] running command.raw on 172.23.106.171: /cygdrive/c/Program\ Files/Couchbase/Server/bin/couchbase-cli.exe group-manage --cluster=172.23.106.171:8091 -u Administrator -p password --add-servers="172.23.106.172:8091;172.23.106.173:8091" --group-name=group2 --server-add-username=Administrator --server-add-password=password
2015-07-01 15:26:34 | INFO | MainProcess | test_thread | [remote_util.execute_command_raw] command executed successfully
2015-07-01 15:26:34 | INFO | MainProcess | test_thread | [remote_util.log_command_output] SUCCESS: add server '172.23.106.172:8091' to group 'group2'
2015-07-01 15:26:34 | INFO | MainProcess | test_thread | [remote_util.log_command_output]
2015-07-01 15:26:34 | INFO | MainProcess | test_thread | [remote_util.log_command_output] ERROR: unable to add server '172.23.106.173:8091' to group 'group2' (400) Bad Request
2015-07-01 15:26:34 | INFO | MainProcess | test_thread | [remote_util.log_command_output]
2015-07-01 15:26:34 | INFO | MainProcess | test_thread | [remote_util.log_command_output] ["Join completion call failed. Got HTTP status 500 from REST call post to http://172.23.106.173:8091/completeJoin. Body was: \"\\\"Unexpected server error, request logged.\\\"\""]
2015-07-01 15:26:34 | INFO | MainProcess | test_thread | [remote_util.log_command_output]
FAIL
2015-07-01 15:26:34 | ERROR | MainProcess | test_thread | [rest_client._http_request] http://172.23.106.171:8091/pools/default/serverGroups/0650d944dd7113fdcd9e98b94f17e74c error 400 reason: unknown

ERROR