Box Sync 4.0 provides detailed user notifications if there is an issue syncing a file or folder.
You will receive this error notification if Box Sync is generating too much traffic to the Box Server. This can happen with large bulk uploads or during periods of increased activity in the folder tree (i.e. rapidly updating many files).
All devices with Box Sync installed.
Typically, Sync will report that the file will be automatically retried after a few minutes. If it does not report this, then try the Retry All button in the Problem Notification.