I am having this problem as well. I am running tuxpoldo's build of btsync (version 1.2.82) on Debian Testing (Linux linux 3.11-2-amd64 #1 SMP Debian 3.11.10-1 (2013-12-04) x86_64 GNU/Linux). The problem is easily reproducable on my machine: # ps aux | grep btsyncjackson 10576 0.2 0.9 942368 76616 ? Sl 12:19 0:04 evince /home/jackson/collections/software/linux/btsync/BitTorrentSyncUserGuide.pdfroot 11381 0.0 0.0 10356 916 pts/1 R+ 12:52 0:00 grep btsync# /usr/lib/btsync/btsync-daemon --nodaemon --config /etc/btsync/default.conftotal physical memory 536870912 max disk cache 2097152Using IP address 192.168.0.100Loading config file version 1.2.82Loaded folder /home/shared/btsync_testError while adding folder /home/shared/btsync_test: Selected folder is already added to BitTorrent Sync.^CReceived shutdown request via signal 2Shutdown. Saving config sync.datHere is my default.conf file (with device_name and secret blanked out for privacy): //// DAEMON_UID=shared// DAEMON_GID=shared// DAEMON_UMASK=0002//{ "device_name": "", "storage_path" : "/home/shared/.btsync", "listening_port" : 0, // 0 - randomize port "check_for_updates" : false, // use apt for updates "use_upnp" : false, // Don't try to talk through NAT "download_limit" : 0, // limits in kB/s "upload_limit" : 0, // 0 = no limits "webui" : {}, // Disable WebUI "shared_folders" : [ { "secret" : "", "dir" : "/home/shared/btsync_test", "use_relay_server" : false, // LAN only "use_tracker" : false, // LAN only "use_dht" : false, // LAN only "search_lan" : true, // Look for sharing computers on LAN "use_sync_trash" : true // Save files deleted on other devices } ]// Advanced preferences can be added to config file.// Info is available in BitTorrent Sync User Guide.}Note that if I delete all the .dat files that btsync creates, it works. But then fails again on the next run: # rm /home/shared/.btsync/*.dat# /usr/lib/btsync/btsync-daemon --nodaemon --config /etc/btsync/default.conf By using this application, you agree to our Privacy Policy and Terms.http://www.bittorrent.com/legal/privacyhttp://www.bittorrent.com/legal/terms-of-usetotal physical memory 536870912 max disk cache 2097152Using IP address 192.168.0.100^CReceived shutdown request via signal 2Shutdown. Saving config sync.dat# /usr/lib/btsync/btsync-daemon --nodaemon --config /etc/btsync/default.conf total physical memory 536870912 max disk cache 2097152Using IP address 192.168.0.100Loading config file version 1.2.82Loaded folder /home/shared/btsync_testError while adding folder /home/shared/btsync_test: Selected folder is already added to BitTorrent Sync.I don't know what the correct behavior should be (ignoring .dat if --config is given, ignoring .dat if webUI disabled in config file, refraining from writing .dat if --config is given, something else ...), but something is definately borked in the current linux implementation.