Network Manager error

Network Manager error

When I run Network manager on my Scientific Linux 6.4, I get:
[root@computer]# nm-applet
** (nm-applet:4157): WARNING **: <WARN> bus_init(): Could not get the
session bus. Make sure the message bus daemon is running! Message: Did
not receive a reply. Possible causes include: the remote application did
not send a reply, the message bus security policy blocked the reply, the
reply timeout expired, or the network connection was broken.
GConf Error: Failed to contact configuration server; some possible causes
are that you need to enable TCP/IP networking for ORBit, or you have stale
NFS locks due to a system crash. See http://projects.gnome.org/gconf/ for
information. (Details - 1: Failed to get connection to session: Did not
receive a reply. Possible causes include: the remote application did not
send a reply, the message bus security policy blocked the reply, the reply
timeout expired, or the network connection was broken.)
An instance of nm-applet is already running.
(nm-applet:4157): GConf-WARNING **: Directory
`/system/networking/connections' was not being monitored by GConfClient
0x9cac60
How can I fix this problem? Thanks in advance.