Hi Joanne76 , that definitely will cause problems, do not try it. Assuming that you have a live cloud file, then probably your users have taken a backup and have opened those files locally. However, each backup is a complete file, therefore if any of them is updated locally, then restored online, it becomes the current (live) file. If another file is restored, it overwrites the current live file. And if the live online file had been changed prior to the restore, those changes would be lost.
MYOB did provide 'checkout' and 'sync' options in earlier versions of AccountRight, but they have been discontinued.