Cash Journal - Payment reversal

Hi,

I have posted a payment through cash journal/cash desk (FPCJ) and closed the the lot. Now I want to reverse the payment however SAP function module 'FKK_CJ_PROHIBIT_RVRSL_OF_DOCS' is throwing an error - 'reversal not performed'. Does anyone know how to reverse a payment document posted through cash journal if it's lot has already been closed ?

Thanks,

Amol