Source type is not compatible, for purposes of assignment,with target type

Hi Friends,

I have copied a standard class into a Z class.

In my Z class instead of

lr_cucopartner TYPE REF TO cl_crm_ic_cucopartner_impl

I have given

lr_cucopartner TYPE REF TO zcl_crm_ic_cucopartner_impl

Now when I execute it gives me an error

Source type \CLASS=CL_CRM_IC_CUCOPARTNER_IMPL is not compatible, for the purposes of assignment, with target type \CLASS=ZCL_CRM_IC_CUCOPARTNER_IMPL

the error comes at the point

lr_cucopartner ?=

me->get_custom_controller( 'CuCoPartner' ).

What is the problem?

Regards,

Raju