Usually you see that problem when you format your sd memory in the wrong way.... I had this trouble too, I was needing to clear my sd memory from my canon camera to use it on another device....but what I didn't knew is that they work on fat system and not fat32...when you choose the format options you always have to make sure you are choosing fat (fat16) otherwise you can kill your sd memory...mine is dead.. I lost my 2gb sd memory...and warranty does not cover human mistakes.....

I know there are some special softwares to format the sd memories at their manufacturer's website usually, maybe you can recover yours.