XA_TRANSACTION JDBC Adaptor error

Hi,
I have successfully configured a JDBC 6.0.3 adaptor (IS 6.1) to (ORACLE 9), using XA_TRANSACTION. When I try to invoke a stored procedure (which works with LOCAL_TRANSACTION version) I get the exception below. The reason for using XA is that I want one flow to start Tx, and another to Commit it later - inside a Process Model.

Any ideas appreciated.

Stack Trace:
com.wm.pkg.art.error.DetailedServiceException: [ART.117.4002] Adapter Runtime (Adapter Service): Unable to invoke adapter service MLGBST.Interface.Sirius.StoredProcedure:sp_OrderCreateUpdateXA.
[ART.114.505] Error while invoking adapter service com.wm.adapter.wmjdbc.services.StoredProcedureWithSignature.
null
at com.wm.pkg.art.error.DetailedServiceException.create(DetailedServiceException.java:125)
at com.wm.pkg.art.error.DetailedServiceException.create(DetailedServiceException.java:116)
at com.wm.pkg.art.error.DetailedServiceException.create(DetailedServiceException.java:103)
at com.wm.pkg.art.ns.AdapterServiceNode.invokeService(AdapterServiceNode.java:665)
at com.wm.pkg.art.ns.ARTNSService.baseInvoke(ARTNSService.java:47)
at com.wm.app.b2b.server.invoke.InvokeManager.process(InvokeManager.java:554)
at com.wm.app.b2b.server.invoke.StatisticsProcessor.process(StatisticsProcessor.java:44)
at com.wm.app.b2b.server.invoke.ServiceCompletionImpl.process(ServiceCompletionImpl.java:221)
at com.wm.app.b2b.server.invoke.ValidateProcessor.process(ValidateProcessor.java:49)
at com.wm.app.b2b.server.ACLManager.process(ACLManager.java:194)
at com.wm.app.b2b.server.invoke.DispatchProcessor.process(DispatchProcessor.java:39)
at com.wm.app.b2b.server.AuditLogManager.process(AuditLogManager.java:384)
at com.wm.app.b2b.server.invoke.InvokeManager.invoke(InvokeManager.java:486)
at com.wm.app.b2b.server.invoke.InvokeManager.invoke(InvokeManager.java:359)
at com.wm.app.b2b.server.ServiceManager.invoke(ServiceManager.java:246)
at com.wm.app.b2b.server.BaseService.invoke(BaseService.java:155)
at com.wm.lang.flow.FlowInvoke.invoke(FlowInvoke.java:324)
at com.wm.lang.flow.FlowState.invokeNode(FlowState.java:580)
at com.wm.lang.flow.FlowState.step(FlowState.java:438)
at com.wm.lang.flow.FlowState.invoke(FlowState.java:403)
at com.wm.app.b2b.server.FlowSvcImpl.baseInvoke(FlowSvcImpl.java:1749)