Using Windows 2008 R2 Server with Bittorent Sync version 1.2.73 As per this thread http://forum.bittorrent.com/topic/25076-failed-to-download-postdownload-cannot-create-a-file-when-that-file-already-exists/ , I too am having this issue where I see "PostDownload: Cannot create a file when that file already exists." logged for numerous files, and the modified file is not sync'd. After turning on logging at the affected machine I see numerous entries such as these that explain why: [2013-11-30 10:10:11.873] TorrentFile: failed to rename \\?\E:\MP07LiveDocBackup\Ahead\4\MRUClients.ini into .SyncOld - 183[2013-11-30 10:10:11.898] Error: \\?\E:\MP07LiveDocBackup\Ahead\4\MRUClients.ini - PostDownload: Cannot create a file when that file already exists. I've restarted BTSync several times and the issue returns, I've examined the process via Procmon and can see that the process is failing when it tries to rename MRUClients.ini to MRUClients.ini.SyncOld . (ReplaceIfExists = False) The .SyncOld file exists from a previous sync. Manually deleting all the .SyncOld files gets things back on track.