Failed to create a form in a window

I'd like to create a form in a window. The form has two combo Field. One is a library comboField and the other is a cell comboField. The two fields are linked by ddHiLinkFields() function.  Before use ddHiLinkFields() function, the form must be instantiated. The instantiation action will cause failure when create the form window. Please refer following code. How to solve this problem?

let((fromLib fromCell formLayout1 win)

fromLib = ddHiCreateLibraryComboField(?name 'fromLib ?callback "ddsUpdateSyncWithForm" ?value "" ?prompt "Library")
fromCell = ddHiCreateCellComboField(?name 'fromCell ?callback "" ?value "" ?prompt "Cell")

formLayout1 = hiCreateFormLayout(
'formLayout1
?items list(fromLib fromCell )
?frame "From"
)

Form1 = hiCreateLayoutForm(
'Form1
"Form1"
formLayout1
?buttonLayout 'OKCancelDef
?unmapAfterCB t
?minSize 400:300
)

hiInstantiateForm(Form1)
ddHiLinkFields(Form1->fromLib Form1->fromCell)

;hiDisplayForm('Form1)
win = hiCreateWindow(
nil
"form"
""
""
nil
Form1
)

hiDisplayWindow(win)
)