These files contain the At Ease Users and Groups databases. It is essential that you back them up regularly. You receive these messages because these files are open if even one At Ease User is connected to the AppleShare/At Ease server.
In order to avoid these messages and successfully back up these files, make sure that all users are logged out of At Ease and set up At Ease so that clients will disconnect from the server when sitting idle at the login screen.
This setting is found under the Maintenance menu in the System Preferences dialog. Also, you can automatically disconnect clients by choosing the "Lock out volumes during backup" option within the Retrospect application.
For more information about this setting, refer to your Retrospect documentation.