I have two Hik vision cameras which both have a serial number of DS-2CD2385FWD. Each one has an SD card installed and recording to it. However, lately the cameras state that the SD card is not installed. We have got round the problem by rebooting the cameras when we notice this has happened but would like to get this resolved so that I don't have to worry. Could you let me know if this is a known problem and if there is a solution for these. Many thanks