installing a new fender

I need to remove my passenger side fender and replace it with the new one i just purchased. I have all the bolts off the old one except the 2 under the black liner that goes from the front wheel to the back wheel. i tried unscrewing the black screws but only one was willing to be removed. all the others just spin in place. can you give me any advice on how to remove this liner or how to get to those 2 bolts so i can finish this job. thanks.

those damn things what they are is plastic screws that strip out you need to hold then with a pair of plyers