Card write protected, how to fix it?

I have a Canon EOS 450D. Last night (after setting up for the lunar eclipse), the camera fell and when i switched it back on it said "card write protected". The tab on the card to protect it hasn't been moved but even after taking the card out and moving the protecrtion tab back and forth it still makes no difference. I can view photos on the card while it's in the camera but it won't let me format the card or take photographs. Anyone else have this problem with an EOS and any ideas how to fix the problem. TIA: