As you say it is a STAND ALONE database (meaning one file, no backend or frontend but all together) you need to split the database anyway. It will help avoid corruption where you will lose all of your data. The frontend should be on each person's computer and the backend on a file server in a folder where everyone who uses the database has read/write/delete permissions.
And to go with what Jeannette wrote, you could have a bad router, bad cable, whatever which causes the computer running it to lose contact with the database file. Hopefully you are NOT trying to run this over a wireless connection. If you are, you'd be way better off not doing that as that drops connection quite frequently compared to a hard-wired system. Also if you must use a wireless connection, you really do need to split the database and have a frontend and backend with the frontend on each computer. That will help avoid corruption and also if one person loses connection and their frontend corrupts you just replace it and in the meantime everyone else can still be working with it.