When an error happens, the sync will try to continue until the end. If one of the bases are disconnected, it will stop.
A common source of errors are hidden system directories like
.Trashes. These directories are usually located at the root of a device or in your home directory. If the error happens on the source, it usually means that you’re trying to backup the entire filesystem (including system directories like
/System which usually don’t hold personal files) or your entire home directory. SyncTime doesn’t have enough privileges to access system directories and is not designed to do a full volume backup; it is recommended that you only backup selected directories inside your home directory. If you still think that you need to backup directories containing one of these system items, you can either exclude hidden files or selectively exclude the system items. If, on the other side, the error happens on the destination, it usually means that the destination is the root of an external device: in this case, in order to avoid these system-created files, you can create an empty directory on the root of the external device and use that as the destination.
Another source of errors can be missing permissions for files like your Photos library, Contacts, Calendar, Reminders and user directories like Desktop, Documents and Downloads. When trying to access one of these locations, you should get a system alert asking for permission. In case you denied any of them, you can enable them in the System Settings under Security and Privacy > Privacy. If necessary, you can exclude the
Two-way syncs can produce a conflict error when, between syncs, a file is modified on more than one base; the problem is that it cannot be determined which file should overwrite the other one.
.DS_Store files can cause this error when the same folder inside two bases is open in the Finder, in which case they should probably be excluded.
It is always recommended to have a look at the error log, which can be opened by clicking the error badge that appears on the right side of the sync item, or from the context menu. The error log provides information about which files caused the error. Particularly for two-way sync items, it is strongly recommended to sync again by carefully going through the confirmation dialog and making sure that no unique file is going to be copied or removed because of the previous error.
When you sync to another computer, such as a network attached storage (NAS), it can happen that the modification date of a copied file is reset by the destination operating system, which may cause subsequent syncs to report that the file still needs to be synced. In some cases, the problem can be solved by making sure that the network volume has both SMB and AFP services enabled and it is mounted with the same username as the account that you’re currently using on your Mac.