xfconfd is NEEDED to start a session.xfconfd isn't running (D-Bus setup problem);
/etc directory is also NEEDED for the Operating System to function.environment variable $XDG_CONFIG_DIRS is set incorrectly (must include "/etc"),
Installed incorrectly !or xfce4-session is installed incorrectly
zepita's experience says it all . . check the md5sum, burn as slow as possible . . .