Went back to 2.6.32-22-generic, since that fixed other issues (LP:459732).

I installed linux-image-2.6.32-22-generic (version 2.6.32-22.36) and linux-backports-modules-wireless-2.6.32-33-generic (version 2.6.32-22.13) and rebooted, then selected
this kernel from the grub list.

The same failure occurs, with the same error message.
However I don't see the message about the bogus regulatory domain on this kernel.
So something has changed there. I haven't messed about with 'wireless-crda', the
version installed is 1.12, installed 2010-04-16.



Here's the timeline of associations and disassociations with 2.6.32-22-generic:

<system boot>
Aug 31 22:43:03 ubuntu kernel: [   25.199388] wlan1: associated

<cron job restarts interface>
Sep  1 00:55:01 ubuntu kernel: [ 7943.304273] wlan1: deauthenticating from 00:04:ed:00:00:00 by local choice (reason=3)
...
Sep  1 00:55:20 ubuntu kernel: [ 7962.289140] wlan1: associated

<failure>
Sep  1 12:10:37 ubuntu kernel: [48479.500014] No probe response from AP 00:04:ed:00:00:00 after 500ms, disconnecting.

<cron job>
Sep  2 00:55:19 ubuntu kernel: [94361.630495] ADDRCONF(NETDEV_UP): wlan1: link is not ready
...
Sep  2 00:55:19 ubuntu kernel: [94361.704978] wlan1: associated
Sep  2 00:55:20 ubuntu kernel: [94361.710490] ADDRCONF(NETDEV_CHANGE): wlan1: link becomes ready

<failure>
Sep  2 06:44:59 ubuntu kernel: [115343.500012] No probe response from AP 00:04:ed:00:00:00 after 500ms, disconnecting.



As I was poking at this, I got  a faster failure, within a few minutes.

Here's the link being established:
Sep  2 21:57:21 ubuntu kernel: [170085.954566] ADDRCONF(NETDEV_UP): wlan1: link is not ready
Sep  2 21:57:21 ubuntu kernel: [170086.021295] wlan1: direct probe to AP 00:04:ed:00:00:00 (try 1)
Sep  2 21:57:21 ubuntu kernel: [170086.023801] wlan1: direct probe responded
Sep  2 21:57:21 ubuntu kernel: [170086.023805] wlan1: authenticate with AP 00:04:ed:00:00:00 (try 1)
Sep  2 21:57:21 ubuntu kernel: [170086.026038] wlan1: authenticated
Sep  2 21:57:21 ubuntu kernel: [170086.026061] wlan1: associate with AP 00:04:ed:00:00:00 (try 1)
Sep  2 21:57:21 ubuntu kernel: [170086.028671] wlan1: RX AssocResp from 00:04:ed:00:00:00 (capab=0x431 status=0 aid=4)
Sep  2 21:57:21 ubuntu kernel: [170086.028674] wlan1: associated
Sep  2 21:57:21 ubuntu kernel: [170086.034310] ADDRCONF(NETDEV_CHANGE): wlan1: link becomes ready

and failing
Sep  2 22:00:37 ubuntu kernel: [170284.500014] No probe response from AP 00:04:ed:00:00:00 after 500ms, disconnecting.



With regard to the regulatory domain, for 2.6.32-22-generic
I see this in 'grep cfg80211 /var/log/kern.log':
 Aug 31 22:43:01 ubuntu kernel: [   16.169152] cfg80211: Calling CRDA to update world regulatory domain
 Aug 31 22:43:01 ubuntu kernel: [   16.673469] cfg80211: World regulatory domain updated:

then nothing further for three days.

With later kernels, I see a lot more chatter. 
Here's the output of  'grep cfg80211 /var/log/kern.log' for 2.6.32-24-generic, <annotated>.

<cron job>
Aug 30 00:55:01 ubuntu kernel: [186302.842327] cfg80211: All devices are disconnected, going to restore regulatory settings
Aug 30 00:55:01 ubuntu kernel: [186302.842333] cfg80211: Restoring regulatory settings
Aug 30 00:55:01 ubuntu kernel: [186302.842336] cfg80211: Calling CRDA to update world regulatory domain
Aug 30 00:55:01 ubuntu kernel: [186302.846620] cfg80211: World regulatory domain updated:
Aug 30 00:55:20 ubuntu kernel: [186321.879945] cfg80211: Ignoring bogus country IE

<failure>
Aug 30 08:43:33 ubuntu kernel: [214414.573252] cfg80211: All devices are disconnected, going to restore regulatory settings
Aug 30 08:43:33 ubuntu kernel: [214414.573258] cfg80211: Restoring regulatory settings
Aug 30 08:43:33 ubuntu kernel: [214414.573261] cfg80211: Calling CRDA to update world regulatory domain
Aug 30 08:43:33 ubuntu kernel: [214414.576633] cfg80211: World regulatory domain updated:

<cron job>
Aug 31 00:55:20 ubuntu kernel: [272721.460713] cfg80211: Ignoring bogus country IE
(nothing futher, which is odd)

<manual ifdown>
Aug 31 22:25:52 ubuntu kernel: [350144.398418] cfg80211: All devices are disconnected, going to restore regulatory settings
Aug 31 22:25:52 ubuntu kernel: [350144.398424] cfg80211: Restoring regulatory settings
Aug 31 22:25:52 ubuntu kernel: [350144.398427] cfg80211: Calling CRDA to update world regulatory domain
Aug 31 22:25:52 ubuntu kernel: [350144.402698] cfg80211: World regulatory domain updated:

<manual ifup>
Aug 31 22:26:01 ubuntu kernel: [350153.140755] cfg80211: Ignoring bogus country IE