Mile,
In case your interested, i got it to work using the following :
Private Sub cboContact_AfterUpdate()
If DCount("BookingID", "tblPersons", "[EventID]=" & Me.EventID) = 0 Then
Me.BookingID = 1
Else
Me.BookingID = DCount("[PersonID]", "[tblPersons]", "[EventID]=" &...