While overriding lookup method on form data source's field it COC is not working for most of the case so everybody is looking after event handlers. But there is one problem in case of that after writing code for event handler its throwing error as "More Than One Form Was Opened at Once for the Lookup Control" as you can see in following screenshot. To resolve this we need to cancel super call to lookup method which is fairly easy to acheive you just need to add following two lines of code in such case 1 2 3 // Cancel the super call of lookup control. FormControlCancelableSuperEventArgs formControlCancelSuper = e as FormControlCancelableSuperEventArgs; formControlCancelSuper.CancelSuperCall(); for example: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 [FormControlEventHandler(formControlStr(PurchTable, ContactInfo_Email), FormControlEventType::Lookup)] public static void ContactInfo_Email_On...