First of all, please find a speaking topic, then state your camera make, model and finally tell us what you have done when the error occurred. That would help us much more to assess the situation. Also, did you have a look in your manual? Most error messages pointing to user errors (the most common error / mistake after all) are explained and described there, including possible solutions. Don't wait for spoonfeeding, learn to help yourself.
Like what others has said... please tell us your camera make, model, etc... we are not psychic, how the hell we know what is happening from such little informations that you have given. Also tell us what have you done prior to receiving this type of error message?