It may be get corrupted or damaged. In this case you have to perform "restore factory setting" of your mobile. If you don't know how to do this then use following steps.
1.First go to mobile's main menu.
2.Now go to setting option.
3.Now click on "restore factory setting"
4.Now tap on restore button. One message window pop up for security code* type default code 12345 in that and press OK
Which memory of your mobile used to store messages? is it Phone memory or Memory card? If you are using Phone memory to store message then you may likely get such type of problem. You have to store messages in your memory card to overcome this problem. If you don't know how to change it* then use following steps.
First go to Menu option -> now go to Messaging option -> now open Options->tap on Settings option -> now select Other option and navigate to memory card.
That's it.
It seems that there is some problem in your mobile's software setting. It may be get corrupted or damaged. In this case you have to perform "restore factory setting" of your mobile. If you don't know how to do this then use following steps.
1.First go to mobile's main menu.
2.Now go to setting option.
3.Now click on "restore factory setting"
4.Now tap on restore button. One message window pop up for security code* type default code 12345 in that and press OK