Hello Mutale,
Put this simple code in the include ZXWOCU07 user-exit IWO10009.
IF caufvd_imp-auart = 'PM02' AND caufvd_imp-gstrp > sy-datum.
MESSAGE: 'For Order type ''PM02'' Basic Start date can not be in future.' TYPE 'E' DISPLAY LIKE 'I'.
ENDIF.
After this no Order of type 'PM02' (Breakdown) will be able to be created with future date in Basic Start date field. It will throw the following error pop-up during such attempts.
Regards
KJogeswaraRao