How to stop Sales transaction with out voucher no

Dear sir,
How to stop Sales transaction with out voucher no when it set to manual numbering.

 

Dear Mr.Kamal,

please try this code ,it may help you!


[#Field : VchNumber]

Control : Customcontrol : $$Isempty:$$Value AND @@Issales

[System : Formula]

Customcontrol : "Dear "+$$CmpuserName"+!!! \n Please Enter Valid Vchno \n It cannot be empty!!"