distributedR_start() problem

Hello all,

I've installed the 0.5 version of DistributedR on CentOS 6.5.
I have one Master and four Workers installed as VMware VMs.

Starting DistributedR in Single Machine Mode works.

Starting DistributedR in Multiple Machine Mode fails.

The output of R is :
> distributedR_start(cluster_conf="/home/jin/dR/cluster.xml", log=3)Workers registered - 0/4. Wait upto 60 seconds.
Shutdown complete
Error in value[[3L]](cond) : No workers are registered


The Master log is :
2014-Apr-13 10:37:13.029405 [INFOR] Master node is listening at 8989 port.2014-Apr-13 10:37:13.029981 [INFOR] Resource Manager Created
2014-Apr-13 10:37:13.030012 [INFOR] Master Initialization done
2014-Apr-13 10:37:14.306944 [INFOR] Master awaiting HELLO handshaking with Workers.
2014-Apr-13 10:38:14.307571 [ERROR] No workers are registered
2014-Apr-13 10:38:14.310596 [DEBUG] Sending Shutdown message to Workers.
2014-Apr-13 10:38:15.315530 [DEBUG] Killed Master Message Handler
2014-Apr-13 10:38:15.315784 [DEBUG] Killed Scheduler
2014-Apr-13 10:38:15.315899 [INFOR] distributedR shutdown complete. 

The Worker log is :
2014-Apr-13 10:37:14.119284 [INFOR] Starting worker.2014-Apr-13 10:37:14.121764 [INFOR] Creating Executors in Worker
2014-Apr-13 10:37:14.122062 [INFOR] Created new Executor 0 with Process ID 2978
2014-Apr-13 10:37:14.122525 [INFOR] Created new Executor 1 with Process ID 2979
2014-Apr-13 10:37:14.123041 [INFOR] Created new Executor 2 with Process ID 2980
2014-Apr-13 10:37:14.123560 [INFOR] Created new Executor 3 with Process ID 2981
2014-Apr-13 10:37:14.129698 [INFOR] Created HandleRequest threads to listen requests from Master
2014-Apr-13 10:37:14.129752 [INFOR] Worker centos2.localdomain:9090 with 4 executors and 1804647628 Shared Memory
2014-Apr-13 10:37:14.176329 [INFOR] Creating a connection for handshake with master centos1:8989
2014-Apr-13 10:37:14.176521 [INFOR] Worker opened connection to Master at centos1:8989
2014-Apr-13 10:37:14.176618 [INFOR] Sending reply with worker info: centos2 9090
2014-Apr-13 10:37:14.176776 [INFOR] HELLO Handshaking reply sent to Master. Master centos1:8989 registered with Worker
2014-Apr-13 10:37:14.228034 [DEBUG] Connected to master at tcp://centos1:8989
2014-Apr-13 10:39:44.195226 [INFOR] Master node is detected to be down. Shutdown worker : elapsed time since last heartbeat: 150
2014-Apr-13 10:39:44.195568 [INFOR] Worker Shutdown triggered.
2014-Apr-13 10:39:44.195850 [DEBUG] Total MB fetched:    0.00 MB
Total fetch time:    0.00 s
Total MB   sent:    0.00 MBTotal send time:    0.00 s
Total cc time:    0.00 s
2014-Apr-13 10:39:44.195931 [DEBUG] PrestoWorker shutdown - joining threads
2014-Apr-13 10:39:44.197261 [DEBUG] PrestoWorker shutdown - joining threads for 0:0
2014-Apr-13 10:39:44.197416 [DEBUG] PrestoWorker shutdown - joining threads for 0:1
2014-Apr-13 10:39:44.197485 [DEBUG] PrestoWorker shutdown - joining threads for 0:2
2014-Apr-13 10:39:44.197538 [DEBUG] PrestoWorker shutdown - joining threads for 0:3
2014-Apr-13 10:39:44.197842 [DEBUG] PrestoWorker shutdown - joining threads for 1:0
2014-Apr-13 10:39:44.198115 [DEBUG] PrestoWorker shutdown - joining threads for 2:0

The cluster.xml file is :
<MasterConfig>  <ServerInfo>
    <Hostname>centos1</Hostname>
    <Port>8989</Port>
  </ServerInfo>
  <Workers>
    <Worker>
      <Hostname>centos2</Hostname>
      <Port>9090</Port>
      <Executors>4</Executors>
      <SharedMemory>0</SharedMemory>
    </Worker>
    <Worker>
      <Hostname>centos3</Hostname>
      <Port>9090</Port>
      <Executors>4</Executors>
      <SharedMemory>0</SharedMemory>
    </Worker>
    <Worker>
      <Hostname>centos4</Hostname>
      <Port>9090</Port>
      <Executors>4</Executors>
      <SharedMemory>0</SharedMemory>
    </Worker>
    <Worker>
      <Hostname>centos5</Hostname>
      <Port>9090</Port>
      <Executors>4</Executors>
      <SharedMemory>0</SharedMemory>
    </Worker>
  </Workers>
</MasterConfig>

Thank you for your help,
Jin