if you are having problems with your memory card then in 80% of the case there is the issue of memory card corruption. The main reason behind this corruption is virus attack, pulling out of memory card while the phone was on, taking photos when the phone's battery is very low, etc. All these issues leads to memory card corruption problems. When this issue occurs you must stop taking the photos and try to recover first the lost photos. YOu can do it by using a good memory card recovery software program. From online you will find numerous.