SOAP - XI - SOAP

When posing a ABAP Proxy as WebService in XI, the tester shows the following message when tested.

<SOAP:Fault>
         <faultcode>SOAP:Server</faultcode>
         <faultstring>failed to call the adapter engine</faultstring>
         <detail>
            <s:SystemError xmlns:s="http://sap.com/xi/WebService/xi2.0">
               <context>XIAdapter</context>
               <code>DeliveryException</code>
               <text>com.sap.aii.af.mp.module.ModuleException
	at com.sap.aii.af.mp.soap.ejb.XISOAPAdapterBean.process(XISOAPAdapterBean.java:753)
	at com.sap.aii.af.mp.module.ModuleLocalLocalObjectImpl3.process(ModuleLocalLocalObjectImpl3.java:103)

When the payload is placed in RWB Send Message, it shows 500 Internal error.

What could be wrong?

-thanks in advance