It is important to remember that, when you add a user-defined field, the database structure is updated. Therefore you should only add new fields when no other users are logged in.
If you try to add a new field, the system will warn you if there are logged in users. You have the option to:
Try Again – you can notify the users close their work and wait until they have logged out of the system
Ignore - the system will force close all open documents for all connected users