No suitable down payment requests exist Message no. F5002

Hi, All

now I'm test the billing plan,

1: create the sales order (normal sales order)

2: check the item billing plan data.

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25.03.2009 0009 Down payment 30.00 2,340.00 CNY 4 C 01 FAZ 0

26.03.2009 0004 Engineering/D 40.00 3,120.00 CNY 02 1 A 01 0

27.03.2009 0007 Operational 60.00 4,680.00 CNY 02 1 A 01 0

28.03.2009 0008 Closing Invoi 0.00 0.00 CNY 02 1 A 01 0

__________ ____ _____ _____________ ___,__ _____________________ _____ __ _ _ ____ __ ____ __.___,_____ ____________

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3: Create the FAZ billing document

4: F-29 , create the customer down payment

but in this step , the system have a error message: "No suitable down payment requests exist Message no. F5002"

I'm don't know which step I missed , Could you help check it,

Thanks.