Are you talking about the side skirts / kick panels? If so, mine did the same thing on both sides. I could see the white clips, but they would not snap in, and it turned out they were just broken. I bought a full new set of white clips and expanding rivets (along the bottom edge, and back edge in rear wheel well), removed both side skirts and reattched with the new "hardware"
Here's the parts diagrams:
#1 Non-Sport:
http://www.realoem.com/bmw/showparts...96&hg=51&fg=20 #2 Sport / M-Technic:
http://www.realoem.com/bmw/showparts...61&hg=51&fg=20 Part #5 in the diagrams are the main white clips that hold the panel to the car. There were 11 (Eleven) needed per side on my Sport/M-Tech model.
Part #7 are grommets the are used with the white clips. But, not a single one came out when I removed the old clips, so they weren't nessesary.
Part #6 are expanding rivets that go on the underside of the skirt. I believe 7 were needed per side. Many old ones were destroyed upon removal.
Part #8 are some more expanding rivets that go on the "ends" of the side skirt. 2 are needed per side for the Sport/M-Tech, and it says the base model needs 4 per side. Every old one was destroyed upon removal.