Yes, I had an issue like this in my main Openbox install yesterday. And I had it once a while, along with other little annoying issues I fixed on the fly.
I looked in the file ~/.xsession-errors, and found a message related to dbus and freedesktop.hal-something. I looked at the web, and saw the answer in big letters all along the google search page : HALD.
I restarted hal, and the problem is gone. We do have a problem with hal, that hangs once a while, and hal is now deprecated, being replaced by udisks.
Your issue may be related or not related to hal as what I met with, anyhow that information can eventually help.
To restart hal:
# /etc/init.d/haldaemon restart
Yesterday I got "FAIL" at the first action, which is "stop", and "OK" at the second action of the restart which is "start" : this showed me that hal was not previously started.
If someone has an idea to fix it anyhow, I'd be interested.
PS: the exact message error was "Error org.freedesktop.DBus.Error.ServiceUnknown: The name org.freedesktop.Hal was not provided by any .service files"
This message copied to google search brings back posts containing messages such as "hald gives Error doing GetSeats on ConsoleKit "
As I had met with haldeamon hang issues, I thought restarting it would to the trick, and it did (If I just type "shutdown" or "reboot" as user, it works, but maybe because I put my user login in the group wheel).