suggest me the reasons for database crash in nav 3.7 db

hi friends,

kindly suggest me on the below issue that we are facing often with nav 3.7 database.

we have implemented LS retail to 2000 stores. The HO database is having nav 4.3 and sql database. All the store db's have nav 3.7, and the store uses native database. we often face an issue that the store nav db crashes ofte, so every time we need to suggest the client on a db rebuild.Can any one suggest me on what could be the possible cause for database crash.

thanks,
Durga