Version 6.0.0 is a cwRsync server focused release, in where we have upgraded Cygwin DLL to the latest 3.x version. Thanks to major changes in Cygwin, cwRsync server doesn't need a dedicated service account any longer and is run by the local system account. A direct upgrade to version 6.0.0 is not supported for the server: You need to uninstall it and install the new one as a fresh installation.