CF Card Error

Having trouble with Canon Digital Elph Powershot S400 and writing to CF card, now all of the sudden keep getting CF Error. I have many sandisk cards and the camera has worked fine for some time. I only use sandisk CF cards and sandisk reader to transfer to my pc. I have used the Powershot S400 format function on my cards. The format function works fine, but when I go to take a picture, the camera take the picture, but once it tries to write to the CF, the camera give the CF Error. I also have a Canon 20D, I have tried the CF cards that are giving me this problem in that camera and they work fine. I also try use the Canon 20D format function. The cards format fine and work fine on the 20d. Any ideas why the Powershot S400 does not like any of the 4 Sandisk CF after months... Any ideas? I have owned my camera now for almost 3 years...

when i put my card in the camera and turn it on the camera says sd door open