prevent user from saving after throwing error message in exit ZXWOCU07( EXIT_SAPLCOIH_009)

hello all,

for a PM Order in transaction IW32 ,

i have written a condition in user exit  ZXWOCU07( EXIT_SAPLCOIH_009),

the condition is throw error message if actual quantity is not equal to zero

when user selects Complete(business) button in application toolbar,

however the issue is after throwing the error , if user clicks enter and select save , the order is getting saved

which should not happen  i.e  it should prevent saving the order after throwing error message,

how do i achieve this,

below is my code in the include,

data : wa_resb TYPE resb,        it_resb TYPE STANDARD TABLE OF resb.
 if  caufvd_imp-auart eq c_ordertype_pm80 and sy-tcode EQ 'IW32'.   if sy-ucomm eq 'ARCH' or sy-ucomm eq 'WTER'.
 select * from resb INTO TABLE it_resb WHERE aufnr eq caufvd_imp-aufnr                                        and enmng GT 0.   if it_resb[] is   NOT INITIAL.     MESSAGE 'The actual Quantities are not zero for this order' type 'E'.   endif.
 endif.
 endif.

thanks in advance....