String StResultat
String StParam
long   ret

SetNull(StResultat)
StParam = "abcd"   - Pour teste

SoapConnection conn
facturesoap    proxy //ServiceProxy is a proxy generated by Web service //wizard

TRY
   conn = CREATE  SoapConnection
   ret = conn.CreateInstance(proxy, "facturesoap")
   IF  (ret <> 0)then
       MessageBox("Fail", "Cannot create proxy "+ "facturesoap")
    ELSE
       //StResultat = proxy.helloworld(StParam)
         StResultat    = proxy.helloworld()
       MessageBox("WebService OK ", "Return String -> '" + StResultat)
   END IF

CATCH (SoapException e1)
       MessageBox("WebService KO SoapException"  , "Invoke Service 'Helloworld'")   
CATCH (PBXRuntimeError e2)
       MessageBox("WebService KO PBXRuntimeError", "Invoke Service 'Helloworld'")
CATCH (RuntimeError e3)
       MessageBox("WebService KO RuntimeError"   , "Invoke Service 'Helloworld'")
END TRY

TRY
         if SQLCA.SQLCODE = 'value' then 
              SQLException = Create Throwable
              SQLException.setmessage("Database ERREUR: " + SQLCA.sqlerrtext )
        end if

et plus loin faire le CATCH