error 2450

[inchong]

When i try to open a form i get this error.

steps:
1. main menu - select a customer form
2. Documents button in the customer form - click to see a document
3. View additional button in Document form
4. select any document and click preview button in Document search
form
5. Document-Additional form opens

In database tab window,
i get this error when i try to open Document-Additional form
Error2450 cannot find the form Document search form.....
but, i don't get this error after opening Document search form first
and open Document-Additional form

is there anything i can do here?
VB code for Document-Additional form
Form_Open(Cancel As Integer)
Dim CurrentDB As String, ssql As String, MyFilter As String

CurrentDB = [Forms]![Document Search Form]![Lease/Docs/DB Name
subform].[Form]![DatabaseName]

Please advise me. thanks.