Might be a little late on this but seem to me your syntax is a little off. Try doing it like this.
If txt1.Text = ("Scott_Atkinson") Then
response = MsgBox("83 new hythe lane, Larkfield, ME20, Kent")
ElseIf txt1.Text = ("James_Ludlow") Then
response = MsgBox("27 Tonbridge road, ME17, Kent")...