Gah. I noticed that this issue was only affecting one access point.
I tried deleting the entry in the edit connections dialogue and
reconnecting to that access point. All worked fine.
I'm not sure what the issue was but all is working fine now anyway.
** Changed in: network-manager (Ubuntu)
** Attachment added: "Dependencies.txt"
http://launchpadlibrarian.net/32126891/Dependencies.txt
** Attachment added: "Gconf.txt"
http://launchpadlibrarian.net/32126892/Gconf.txt
** Attachment added: "IfupdownConfig.txt"
http://launchpadlibrarian.net/32126893/IfupdownConfig.txt
** Attac