I have a Canon xsi and I when I turned it on my screen read "Card Write Protected" so I checked my other SD cards (I have two 8GB, one 16GB and one 4 GB) and all of them said this. I use my camera frequently so I don't know why this suddenly started happening. Yes, I check for the damn lock on the side of the SD card and it is NOT nor was it in the Lock position. I also put the SD card in my computer and checked "Properties" and made sure it wasn't "Read Only". I am still having this problem so if anyone has a solution, please help!
Alright, so I made sure the little switch on the side wasn't in "Lock" position and I made sure the preferences were right while on my computer and if I try to edit the card (ie: format card) with my camera it says "Card Write Protected" Also, I tried all four SD cards in a different camera and they all work fine. Therefore, it must be a Camera-specific problem. I still need a solution, I feel lost without my DSLR!