HTTPRequest throw HessianRuntimeException

Hi ,
I submit a httprequest in soapUI 3.5.1 and sometimes i can submit successfully,but sometimes will throw out below error, can some body tell me root cause of this error.thank you very much !

com.caucho.hessian.client.HessianRuntimeException: java.net.ConnectException: Co
nnection timed out: connect
at com.caucho.hessian.client.HessianProxy.sendRequest(HessianProxy.java:
263)
at com.caucho.hessian.client.HessianProxy.invoke(HessianProxy.java:151)
at $Proxy0.getDate(Unknown Source)
at com.webex.gemini.soapui.GeminiLogPanel.getServerTime(GeminiLogPanel.j
ava:98)
at com.webex.gemini.soapui.GeminiLogPanel.setEndTime(GeminiLogPanel.java
:110)
at com.eviware.soapui.impl.support.panels.AbstractHttpRequestDesktopPane
l.afterSubmit(AbstractHttpRequestDesktopPanel.java:562)
at com.eviware.soapui.impl.wsdl.panels.teststeps.HttpTestRequestDesktopP
anel.afterSubmit(HttpTestRequestDesktopPanel.java:337)
at com.eviware.soapui.impl.wsdl.WsdlSubmit.run(WsdlSubmit.java:150)
at com.eviware.soapui.impl.wsdl.WsdlSubmit.submitRequest(WsdlSubmit.java
:75)
at com.eviware.soapui.impl.support.http.HttpRequest.submit(HttpRequest.j
ava:260)
at com.eviware.soapui.impl.wsdl.teststeps.HttpTestRequestStep.run(HttpTe
stRequestStep.java:254)
at sun.reflect.GeneratedMethodAccessor354.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAcces
sorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.codehaus.groovy.runtime.callsite.PojoMetaMethodSite$PojoCachedMet
hodSiteNoUnwrapNoCoerce.invoke(PojoMetaMethodSite.java:229)
at org.codehaus.groovy.runtime.callsite.PojoMetaMethodSite.call(PojoMeta
MethodSite.java:52)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCa
llSite.java:129)
at Script1.run(Script1.groovy:312)
at com.eviware.soapui.support.scripting.groovy.SoapUIGroovyScriptEngine.
run(SoapUIGroovyScriptEngine.java:93)
at com.eviware.soapui.impl.wsdl.teststeps.WsdlGroovyScriptTestStep.run(W
sdlGroovyScriptTestStep.java:148)
at com.eviware.soapui.impl.wsdl.panels.teststeps.GroovyScriptStepDesktop
Panel$RunAction$1.run(GroovyScriptStepDesktopPanel.java:274)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExec
utor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor
.java:908)
at java.lang.Thread.run(Thread.java:619)
Caused by: java.net.ConnectException: Connection timed out: connect
at java.net.PlainSocketImpl.socketConnect(Native Method)
at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:333)
at java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:195)
at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:182)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:366)
at java.net.Socket.connect(Socket.java:525)
at java.net.Socket.connect(Socket.java:475)
at sun.net.NetworkClient.doConnect(NetworkClient.java:163)
at sun.net.www.http.HttpClient.openServer(HttpClient.java:394)
at sun.net.www.http.HttpClient.openServer(HttpClient.java:529)
at sun.net.www.http.HttpClient.<init>(HttpClient.java:233)
at sun.net.www.http.HttpClient.New(HttpClient.java:306)
at sun.net.www.http.HttpClient.New(HttpClient.java:323)
at sun.net.www.protocol.http.HttpURLConnection.getNewHttpClient(HttpURLC
onnection.java:860)
at sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConne
ction.java:801)
at sun.net.www.protocol.http.HttpURLConnection.connect(HttpURLConnection
.java:726)
at sun.net.www.protocol.http.HttpURLConnection.getOutputStream(HttpURLCo
nnection.java:904)
at com.caucho.hessian.client.HessianProxy.sendRequest(HessianProxy.java:
261)
... 23 more