D40 problem with cards

I've searched but not found my particular problem:

I am getting a "card cannot be used..." error message with all my SD cards in my D40. At first I thought it was a particular card but it's not - it happens with all 4 of my cards. The cards are of varying ages and makes. I might get several shots before the error. All the cards have been formatted in camera to no avail.

Before I send the camera to Nikon for repairs, is there anything else I can try?

Thanks for taking the time to help.

LindaJ