Have you tried restarting the LXPanel? Lubuntu has Default applications for LXsession. Make sure that the Launcher Manager is lxpanelctl. I don't know how it could have been changed or deleted but I would check there first. Also if your menu is empty look here, http://wiki.lxde.org/en/LXPanel#Fix_empty_menu_in_LXPanel. It will It will kill lxpanel, delete the current menu cache and start the panel again.
– RexMay 05 '16 at 16:50