Memory card error/card locked. i just got a sandisk 4.0gb memory card. everytime i put it into my

Question

i just got a sandisk 4.0gb memory card. everytime i put it into my powershot sd600, i got the memory card error and card locked message. i also cannot format (it is blacked out). i also do not have a card reader. my other memory card (kingston 256 mb), which i've had for years still works. please offer advice and suggestions!