Why a PROGRAM ERROR?

[Rusnak <bogus@nowhere.com>]

I have the following code  in a generic package (or code similar to it
anyway):


      Given a tagged type "My_Instance" and a type defined as

          type My_Class_Object_Type is access all My_Instance'Class;

    I have a function in the spec/body, defined in the body as

          function Unpack(The_Object : access My_Instance'Class)
                                      Core_Text : String)
         return Command_Object
         is
            Return_Value :  Command_Object;
        begin
            . . .
               Command_Object.The_Object :=
My_Class_Object_Type(The_Object);
           . . .
         end Unpack;


        Any time I try to cast the anonymous access type to
My_Instance'Class to the type My_Class_Object_Type,
        a program error is raised.  Why is this the case, why is the
error not caught at compile time, and how can I resolve
       the error?  It seems to only occur  when a cast like this one is
made inside an instantiation of a generic package.

       Any help is greatly appreciated.

      If you wish to contact me by e-mail my e-mail id is "jrusnak" and
my ISP is "netgate.net".

    Thanks

-John