Hi, we purchased two 4GB Sony MS Pro Duo memory cards off ebay, to be used in a Sony digital camera, but for some reason the camera is unable to format it

when turning the camera on it just displays "format error" on both cards

I have also tried using Windows to format via USB and it starts to format then displays "Windows is unable to format" when it finishes
I have also tried formatting on the PSP and still have no joy
One of the 2 cards was definately second hand as it contained 2.97GB of PSP stuff on it, and at the time it actually worked .. until I attempted to format it, and now it no-longer works at all
Just to prove that the formatting works, I put in my old 1GB card and formatted it fine
Is there anything I am doing wrong, or are they faulty cards ??
Sorry if this is in the wrong section