Check the following:
1. Have you tried 'downloading' from the camera's memory card to your PC (by connecting the camera to your PC - p.40 in the User Guide) in case the memory card is full or to see how much space is available on your card?
2. Checked that your CF card is not 'locked'. ''Some, not all'', CF cards have a 'write' protection switch which prevents data being written to the card. If your card has one it will be quite obvious to see. Here is an example, (the switch is below the letter 'B' in 16GB)
Here is a link which states which CF cards are suitable for use in a Coolpix E5700. Be aware of the following which is stated in the link:
Other brands and capacities of cards may work, but Nikon cannot guarantee their operation. Check with the manufacturer of the third-party card for compatibility information. Nikon recommends keeping one of the approved cards available for troubleshooting.
3. Have you 'formatted' the CF card in the camera?
Here is a link to the User Guide, scroll to p.135 for an explanation on how to do this.