Are you trying an OTA download? I got that error message with the Bible programs I was downloading. The one program I tried several times and it finally worked. The second one I took the battery out and rebooted and that seemed to work. Good luck.
Most likely, you have too many pictures stored on the device. Try installing a media card and moving the pics over (unfortunately, one by one) or delete the pics and try the download again. You should also change the default size of your pics from Large to Small. (Camera > Menu Button > Options) This will save suffificent space.