I agree with TW1, have you been trying to undo the wrong ones? I have re-attached my undertray this afternoon! Starting at the back, there are two vertical 10mm bolts; moving forward, there are two horizontal 13mm bolts on each side of the metal frame. These are close together and attach the metal frame at an angle of 45 degrees. There are two 13mm bolts that hold the frame at the front along with several screws that hold the bumper valance to the undertray. There are several rivets that hold the plastic part to the main frame of the undertray! These should not be removed! In the Haynes, on page 1A 6, it shows you the location of the bolts. Are you saying that there bolts are not there and the undertray has been rivetted on? My FL is an 05 model and I can't believe that your car would be that different!