Ubuntu 12.04 upgrade - now get Internal Ubuntu Error

I upgraded my Ubuntu with LXDE to 12.04. When I start the network manager manually ("service network-manager start"), a window pops up saying:

Sorry, Ubuntu 12.04 has experienced an internal error

executable path:
/usr/lib/notification-daemon/notification-daemon

package:
notification-daemon.0.7.3-1

title:
notification-daemo crashed with signal 5 in g_return_if_fail_warning()

In another thread, barnacle said

Originally Posted by barnac1e Apparently it has to do with themes. Like the colors, shades, window borders,etc. From what I can tell Ubuntu switched from gtk2 to gtk3 for version 12.04s. Gtk just stands for Gimp Toolkit I think. It was used in designing the window looks and feel in GNOME and Metacity- Gnomes Window Manager. So my guess is somewhere in your settings in from your old Ubuntu is clashing with the new Ubuntu settings. You said you have LXDE on top of Ubuntu? Or do you have the distibution Lubuntu? I think a theme from LXDE is gtk2 based and Ubuntu 12.04 with all gtk3 doesnt like it.

I have LXDE on top of Ubuntu. What do I do to fix this?

Downgrade notification Daemon

@WantLinuxHelp

Did you by chance try those packages and install them?

By the way, if you really still think its the networking though, another easy suggestion is to run as root:

nano -w /etc/group

and find the group in the list for "netdev" and put your username right next to the colon (no spaces between the colon and your username. You can also add yourself to maybe the daemon group, adm, and whatever else applies. Hit cntl+x, then enter and then try and reboot and see if it helps.