I hope it is not a stuck delete button. It could obviously be a timer delete feature either in the camera settings or a glitch in the firmware.
1) Read the manual section pertaining to this.
2) If 1) does not resolve the issue, refer to Nikon Inc. They have a very good tech support dept for their products. Usually you ask the question via email and they will respond. I have used this service for my Nikon D70s.