SysDictField object not initialized

Hi All,

can you help me out to solve this it is not allowing to change the qty and i had compiled but there is no error in these classes.

(C)\Classes\PriceDiscPolicyDialog\createDialogFields - line 51
(C)\Classes\PriceDiscPolicyDialog\dialog - line 46
(C)\Classes\RunBase\dialogMake - line 15
(C)\Classes\RunBase\promptPrim - line 23
(C)\Classes\RunBase\prompt - line 12
(C)\Classes\PriceDiscPolicyDialog\runPolicyDialog - line 20
(C)\Data Dictionary\Maps\PriceDiscResultFields\Methods\runPriceDiscPolicyDialog - line 54
(C)\Data Dictionary\Tables\PurchLine\Methods\runPriceDiscPolicyDialog - line 15
(C)\Classes\PurchLineType\purchQtyAllowEdit - line 9