Exception :"CAST-ERROR" while calling custom BADI

hi experts...we are using SAP ECC 6.0 version

I have created BADI Def and Implementation using se18 and se19 with some interface methods..

Problem:

I'm writing a report to call that using class CL_EXITHANDLER but it shows an Exception..

" Exception condition "CAST-ERROR" raised."

Report example:

 DATA: CL_EXIT  TYPE REF TO CL_EXITHANDLER,
      IF_USER_INSTANCE TYPE REF TO ZIF_EX_USER_MAILID1.
 
CALL METHOD cl_exithandler=>get_instance
  EXPORTING
   EXIT_NAME                       = 'ZBADI_USERMAIL_DEF'
*    NULL_INSTANCE_ACCEPTED        = SEEX_FALSE
*  IMPORTING
*    ACT_IMP_EXISTING              =
  CHANGING
    instance                       = IF_USER_INSTANCE
*  EXCEPTIONS
*    NO_REFERENCE                  = 1
*    NO_INTERFACE_REFERENCE        = 2
*    NO_EXIT_INTERFACE             = 3
*    CLASS_NOT_IMPLEMENT_INTERFACE = 4
*    SINGLE_EXIT_MULTIPLY_ACTIVE   = 5
*    CAST_ERROR                    = 6
*    EXIT_NOT_EXISTING             = 7
*    DATA_INCONS_IN_EXIT_MANAGEM   = 8
*    others                        = 9
        .
IF sy-subrc  0.
* MESSAGE ID SY-MSGID TYPE SY-MSGTY NUMBER SY-MSGNO
*            WITH SY-MSGV1 SY-MSGV2 SY-MSGV3 SY-MSGV4.


 

so i found that all EXITs are in the Table " SXS_ATTR"

but what i have created Classical BADI so it gets an Exception(while i'm debugging found this)

so kindly tel me whats problem of my custom BADI "ZBADI_USERMAIL_DEF" .

but in Implentation class its working fine..