WSO2 Unexpected EOF in prolog - http

Question

I have a proxy that calls another local proxy in WSO2 ESB 4.6.0.
Basically, the definition is:
<proxy name="Proxy1" >
<target>
<inSequence>
<xslt/>
<header name="Action" value="issueActivity" />
<send>
<endpoint>
<address uri="http://localhost:8280/services/Proxy2" format="soap11"/>
</endpoint>
</send>
</inSequence>
<outSequence>
<filter xpath="not(get-property('FAULT'))">
<xslt/>
</filter>
<send />
</outSequence>
</target>
</proxy>
<proxy name="Proxy2">
<target>
<inSequence>
<xslt />
<property name="DISABLE_CHUNKING" value="true" scope="axis2"/>
<send>
<endpoint key="Inbound" />
</send>
</inSequence>
<outSequence>
<filter xpath="get-property('FAULT')">
<then>
<sequence key="DefaultErrorSequence" />
<header name="To" action="remove" />
</then>
<else>
<property name="Content-Encoding" scope="transport" action="remove"/>
<xslt/>
</else>
</filter>
<send />
</outSequence>
</target>
</proxy>
In almost all calls, the flows works perfectly but, periodically, this error appears in the log when Proxy1 try to call Proxy2:
TID: [0] [ESB] TID: [0] [ESB] [2014-05-08 12:03:35,431] WARN {org.apache.synapse.transport.passthru.TargetHandler} - Receiving response while the handler is in an inconsistent state REQUEST_HEAD
TID: [0] [ESB] TID: [0] [ESB] [2014-05-08 12:03:35,432] ERROR {org.apache.synapse.transport.passthru.util.RelayUtils} - Error while building Passthrough stream
org.apache.axiom.om.OMException: com.ctc.wstx.exc.WstxEOFException: Unexpected EOF in prolog
at [row,col {unknown-source}]: [1,0]
at org.apache.axiom.om.impl.builder.StAXOMBuilder.next(StAXOMBuilder.java:296)
at org.apache.axiom.soap.impl.builder.StAXSOAPModelBuilder.getSOAPEnvelope(StAXSOAPModelBuilder.java:204)
at org.apache.axiom.soap.impl.builder.StAXSOAPModelBuilder.<init>(StAXSOAPModelBuilder.java:154)
[...]
At the end of the error in the log:
TID: [0] [ESB] TID: [0] [ESB] [2014-05-08 12:04:35,435] WARN {org.apache.synapse.transport.passthru.TargetHandler} - Connection time out while in state: REQUEST_DONE
TID: [0] [ESB] TID: [0] [ESB] [2014-05-08 12:04:35,436] WARN {org.apache.synapse.FaultHandler} - ERROR_CODE : 101507
TID: [0] [ESB] TID: [0] [ESB] [2014-05-08 12:04:35,436] WARN {org.apache.synapse.FaultHandler} - ERROR_MESSAGE : Error in Sender
TID: [0] [ESB] TID: [0] [ESB] [2014-05-08 12:04:35,437] WARN {org.apache.synapse.FaultHandler} - ERROR_DETAIL : Error in Sender
TID: [0] [ESB] TID: [0] [ESB] [2014-05-08 12:04:35,437] WARN {org.apache.synapse.FaultHandler} - ERROR_EXCEPTION : null
According the WSO2 documentation, the error 101507 means Connection canceled.
The question is what the cause of this error? It's a problem with client or server?
UPDATE
Aparently, the cause of the error is the same described in this question: WSO2 ESB unknown error code 102511

Answer 1

Have you make Return Request Status checkbox enable at operation section while writing query? This may cause the problem..Try it..

Answer 2

To sum up the all comments so far, I think first achievement was that the problem was solved when instead of Proxy1->Proxy2 architecture, changing the Proxy2 to sequences and call them with Sequence mediator instead of invoking them with send mediator removes the errors previously has been shown.
That worked properly but since we need to have the Proxy1->Proxy2 architecture, I think defining the "outSequence" of Proxy1 as receiving sequence in "inSequence" of Proxy1 and sending it to Proxy2 using Send mediator with Proxy2 endpoint would be the solution.