Thanks for writing. In my frmInitial, I have the following code for my date combo box:
If Now() > AsOfDate Then
DoCmd.OpenForm "frmInputForm", , , "[AsOfDate]=" & "#" & Me![cboExistingData] & "#", acFormReadOnly
MsgBox "This form is read only"
Else
DoCmd.OpenForm "frmInputForm", , ...