Open a form in Edit mode using VBA

Hi

Can anyone figure why when I open a form in Access 2007 using VBA code, it will not allow the record to be edited?

I have two forms. The first one, which is a split Form, and the second one which is a datasheet. I have added a button on the first form so that when selected it will run the code which displays an inbox so the user can enter a ID number, then it opens the second form and filters the form to show only the id number entered. However when the form opens the records in it can not be edited. The code I am using is below:

Dim Num As String

Num = InputBox("Please enter the box number you wish to edit?", "Edit Member files")

DoCmd.OpenForm "CFS-ScanningFiles-Claims-Edit", acNormal, , "[BoxNumber]=" & Num, acFormEdit, acWindowNormal

I have checked the properties of the second screen and there is no record lock, and the permissions are set to allow edits. Is it because I am filtering the data?

Can anyone help??

Thank you in advanced

Jeskit