I've tried to download a manual for this camera to give you the most accurate answer possible, however after a few minutes of frustration I'm going to answer this sort of "off the top of my head so to speak" My first impression is that the 4GB memory card my be beyond your cameras capabilities but first try this. Have you checked the memory card to make sure it's not locked I'll include a diagram check the small circle for the correct orientation the arrow shows the lock position.
Once you have made sure the card is unlocked install the memory card and then format the card. Formatting "programs and new card to work with the camera it has been installed into. Also Formatting should be done after each download of pictures to the computer hard drive. In this case formatting cleanse the old pictures off and programs the card once again to give optimum performance between the camera and memory card. If this still doesn't work then I suspect the 4GB card is to large for the camera "firmware and you will need to update your camera on the Samsung web site to a newer version of firmware. Sounds complicated but heck i did it so it's not all that technical. Also the memory card you are replacing may only need to be formatted to begin to work properly again (that's if you were having problems)