No hotkeys in Xfce 4.6

Normally the key combination Alt-f2 in xfce starts the command xfrun4 but some time it stopped working. Checking in Xfce Settings Manager > Keyboard > Application shortcuts found that the key was associated with the correct command, so determined to solve the problem I discovered that the devil xfce4-settings-helper was turned off after launch from the console and restart the session all has returned to normal.