Look inside the SD card socket in the camera (use a flashlight) and check if all the pins are OK, check for misaligned, bended or corroded pin(s). The problem could be caused by a bad contact from the SD card to the connector pins.
What size SD card are you trying to use? I believe that model can't use a SD card larger than 2GB. If it's greater than 2GB, it uses a different memory format and cannot be read.
