The idltojava compiler does not translate the following IDL code to Java correctly.

module Test
{
interface Callback
{
boolean update() ;
} ;

interface Server
{
boolean registerCallback(in Callback monitor) ;
} ;
} ;

The Java code produced for the Server implementation (_ServerImplBase.java) uses the following to implement the registerCallback() method:
           case 0: // Test.Server.registerCallback
                  {
                      boolean __result = self.registerCallback(
                        (Test.Callback)o[0]);
                        n[0] = (__result) ? 1 : 0;
                  }
                   break;
Parameter zero (o[0]) is not a Test.Callback object, hence the cast throws an exception. The exception is reported to the client as an Unknown exception number three.