IPhone pictures?

Asked by glitterrrrfish (222) September 20th, 2008 from iPhone

I’ve had upto 600 pictures on my camera roll, but today I had only 400 and I was about to take a picture but a pop up came up saying I had too many pictures and have to delete some. I deleted and deleted until I had about 315 pictures left and it still wouldn’t let me take additional pictures. Yet I still have 4 GB of free space
Why is this happening and what should I to??