Box Sync 4.0 provides detailed user notifications if there an issue syncing a file or folder.
If a collaborator has locked a file using another application, you will not be able to update the file until the file is unlocked by that application.
All devices with Box Sync installed.
Go to the application and unlock the file. If required, contact the file owner to coordinate your changes. Once this file is unlocked by the application, use the "Retry All" button found in problem file window.