My camera is doing the same with the same error messages and I haven't used hardly any of my memory. I've got about 5 pictures on it. I tried deleting even a few of them but to no avail.
Probably a dumb question, but do you have enough memory available?
If you have been saving pictures to phone memory, you may have filled it to the point where there is no longer enough memory available to run the camera. Try moving your pictures (and/or music files etc) to the memory card. Alternatively, you could move them to the PC using the option to delete them from the phone.