Description of problem:
when I want to install Fedora from usb

Version-Release number of selected component:
anaconda-20.25.15-1.fc20.x86_64

The following was filed automatically by anaconda:
anaconda 20.25.15-1 exception report
Traceback (most recent call first):
  File "/usr/lib/python2.7/site-packages/dbus/connection.py", line 651, in call_blocking
    message, timeout)
  File "/usr/lib/python2.7/site-packages/dbus/proxies.py", line 145, in __call__
    **keywords)
  File "/usr/lib/python2.7/site-packages/dbus/proxies.py", line 70, in __call__
    return self._proxy_method(*args, **keywords)
  File "/usr/lib64/python2.7/site-packages/pyanaconda/ui/gui/spokes/network.py", line 80, in getNMObjProperty
    prop)
  File "/usr/lib64/python2.7/site-packages/pyanaconda/ui/gui/spokes/network.py", line 860, in _add_ap
    mode = getNMObjProperty(ap_dbus, ".AccessPoint", "Mode")
  File "/usr/lib64/python2.7/site-packages/pyanaconda/ui/gui/spokes/network.py", line 722, in _refresh_ap
    self._add_ap(ap, active)
  File "/usr/lib64/python2.7/site-packages/pyanaconda/ui/gui/spokes/network.py", line 640, in refresh_ui
    self._refresh_ap(device, state)
  File "/usr/lib64/python2.7/site-packages/pyanaconda/ui/gui/spokes/network.py", line 361, in on_device_selection_changed
    self.refresh_ui(device)
DBusException: org.freedesktop.DBus.Error.UnknownMethod: Method "Get" with signature "ss" on interface "org.freedesktop.DBus.Properties" doesn't exist


Additional info:
cmdline:        /usr/bin/python  /sbin/anaconda --liveinst --method=livecd:///dev/mapper/live-base
cmdline_file:   BOOT_IMAGE=/syslinux/vmlinuz0 root=live:LABEL=LIVE rw rd.live.image rd.live.overlay=LABEL=LIVE quiet rhgb
executable:     /sbin/anaconda
hashmarkername: anaconda
kernel:         3.11.10-301.fc20.x86_64
other involved packages: dbus-python-1.2.0-1.fc20.x86_64
product:        Fedora
release:        Fedora release 20 (Heisenbug)
type:           anaconda
version:        20