I had this problem last night. The cause in my case was that I changed the network password from another machine, and the machine that the problem was on was left on all night. When I got to it in the morning there were many dozens of "Wifi network identification required" dialogue windows open, which indeed won't go away very quickly. nm-applet is using a whole core all to itself, and not doing a lot. The wifi is in the meantime connected, but the dialogue boxes will not go away.
I had this problem last night. The cause in my case was that I changed the network password from another machine, and the machine that the problem was on was left on all night. When I got to it in the morning there were many dozens of "Wifi network identification required" dialogue windows open, which indeed won't go away very quickly. nm-applet is using a whole core all to itself, and not doing a lot. The wifi is in the meantime connected, but the dialogue boxes will not go away.
This is Ubuntu 13.10, 64bit.