Hi Kiwigirl007,
I hope I have this correct, but I think this is the only code required.
Private Sub LOC_Click()
On Error GoTo Err_ConfirmationLetter_Click
DoCmd.OpenReport "ConfirmationLetter", acPreview, , "[RegistrationID]=" & Forms![Attendees]![Attendees Subform].Form![RegistrationID]...