I've also noticed that sync computers running is read only mode are leaving files when the master computer has removed them. Both computers are connected with OpenVPN and I'm using WinMerge to check the folders are identical http://winmerge.org/ Once I have compared the folders, winmerge (from the view menu) shows a list of "Different Items" "Left Unique Iteme" "Right Unique Items" "Skipped Items" As I'd expect we see .SyncID & .SyncIgnore are different, however I get a list of files that are unique to the computer that is in read only sync mode. If I manually delete them then sync brings them back but with a zero file length as the file doesn't exists on the main computer. If I stop sync on both computers, then delete the files and start sync up again the problem goes away. I also noticed that sync is clever, if you move a file from one folder to another and rather than delete it and re transfer. If simply moves it aswell. I don't know but I think the files I am having problems with are ones that are being moved. I will check next time the error occurs.