Mathieu, here’s a backtrace hopefully with what you requested for (with network-manager-gnome-dbgsym installed).

This is a laptop where I’ve previously connected to another wireless network (over a different router of the same model) successfully.

Now with a different router operating in another broadband connection, when I try to connect to the wifi it provides, nm-applet disappears from indicator area. If I run it from the command-line it outputs this:

jani@amilo:~$ nm-applet
Gtk-Message: Failed to load module ”canberra-gtk-module”
** Message: applet now removed from the notification area
** Message: No keyring secrets found for ElisaKoti48/802-11-wireless-security; asking user.
**
ERROR:nm-utils.c:1231:nm_utils_security_valid: assertion failed: (have_ap)
Aborted

Note that it doesn’t actually ask me for the key but apparently fails when trying to do so. With the previous wireless network I was in, the key *was* requested, and the file describing that connection is still in /etc/NetworkManager/system-connections/.

After doing the above once, there’s also a definition for the non-functioning connection in /etc/NetworkManager/system-connections/, and all subsequent tries to start nm-applet immediately end in the error and the applet vanishing. If I delete the definition it has created for this non-functioning connection, the applet does appear again, but again when I try to connect to this network, it dies and won’t come back until I rm the definition file.