Cannot add servers into an existing cluster (via Cuchbase Server UI)

After setting up two Couchbase servers separately using the UI, one cannot be added to the other server (cluster) with clicking the "add server" button.

The error window appeared with an error message like "This node cannot add another node(n_1@.....) because of cluster version compatibility mismatch (1=/=0).
(screen shot is attached). The ns_server log also reported a crash below:

[error_logger:error] [2012-04-11 9:33:11] [n_0@10.17.8.122:error_logger:ale_error_logger_handler:log_msg:76] ** Generic server ns_doctor terminating
** Last message in was {get_node,'n_0@10.17.8.122'}
** When Server state == {state,{dict,0,16,16,8,80,48,
                                     {[],[],[],[],[],[],[],[],[],[],[],[],[],
                                      [],[],[]},
                                     {{[],[],[],[],[],[],[],[],[],[],[],[],[],
                                       [],[],[]}}},
                               undefined,undefined,undefined}
** Reason for termination ==
** {badarg,[{dict,fetch,
                  ['n_0@10.17.8.122',
                   {dict,0,16,16,8,80,48,
                         {[],[],[],[],[],[],[],[],[],[],[],[],[],[],[],[]},
                         {{[],[],[],[],[],[],[],[],[],[],[],[],[],[],[],
                           []}}}]},
            {ns_doctor,handle_call,3},
            {gen_server,handle_msg,5},
            {proc_lib,init_p_do_apply,3}]}

[error_logger:error] [2012-04-11 9:33:11] [n_0@10.17.8.122:error_logger:ale_error_logger_handler:log_report:72]
=========================CRASH REPORT=========================
  crasher:
    initial call: ns_doctor:init/1
    pid: <0.3888.0>
    registered_name: ns_doctor
    exception exit: {badarg,
                        [{dict,fetch,
                             ['n_0@10.17.8.122',
                              {dict,0,16,16,8,80,48,
                                  {[],[],[],[],[],[],[],[],[],[],[],[],[],[],
                                   [],[]},
                                  {{[],[],[],[],[],[],[],[],[],[],[],[],[],[],
                                    [],[]}}}]},
                         {ns_doctor,handle_call,3},
                         {gen_server,handle_msg,5},
                         {proc_lib,init_p_do_apply,3}]}
      in function gen_server:terminate/6
    ancestors: [ns_server_sup,ns_server_cluster_sup,<0.59.0>]
    messages: [{'$gen_call',{<0.756.0>,#Ref<0.0.0.61012>},get_nodes}]
    links: [<0.717.0>,<0.3889.0>,<0.60.0>]
    dictionary: []
    trap_exit: false
    status: running
    heap_size: 377
    stack_size: 24
    reductions: 1349
    neighbours: