Comment 2 for bug 1311606

If I understand you correctly, it sounds like you have indicator-appmenu installed and enabled. Unfortunately this isn't a configuration we can support in 14.04 - it will consistently crash the panel.

The workaround is to hide indicator-appmenu:

1. Right click the indicator plugin and click properties
2. Click "hide" next to "Application Menus (Global Menu)"
3. Restart the panel: xfce4-panel -r

If you still get crashes after hiding appmenus and restarting the panel, please report it here. Hiding it prevents the crashes in all our testing configurations but there might be some corner cases.