Hi Wil Wu,
Thank you for your response,
These are the result of Infolog message:
(C)\Classes\Info\add 62
(C)\Classes\Global\error 3
(C)\Classes\FormLetterServiceController\afterOperation 14
(C)\Classes\SysOperationServiceController\run 70
(C)\Classes\FormLetterServiceController\run 3
(C)\Classes\PurchFormLetter\run 45
(C)\Classes\PurchFormLetter\main 76
(C)\Classes\FormFunctionButtonControl\Clicked 0
But still I cannot find the error message "0.00 cannot be picked because....".