Same problem with proposed kernel
I suppose the problem is in disasocciating:
wlan0: disassociating by local choice (reason=3)

[  208.616629] ------------[ cut here ]------------                                                                     
[  208.616645] WARNING: at /build/buildd/linux-backports-modules-2.6.27-2.6.27/debian/build/build-generic/compat-wireless-2.6/net/mac80211/main.c:227 ieee80211_hw_config+0xac/0xb0 [lbm_cw_mac80211]()                                         
[  208.616653] Modules linked in: aes_x86_64 aes_generic ecryptfs af_packet rfcomm sco bridge stp bnep l2cap bluetooth ppdev acpi_cpufreq cpufreq_stats cpufreq_conservative cpufreq_ondemand cpufreq_userspace cpufreq_powersave freq_table container pci_slot sbs sbshc iptable_filter ip_tables x_tables sbp2 parport_pc lp parport loop joydev arc4 ecb crypto_blkcipher uvcvideo compat_ioctl32 iwlagn sdhci_pci videodev acer_wmi iTCO_wdt iTCO_vendor_support v4l1_compat sdhci iwlcore mmc_core serio_raw rfkill evdev snd_hda_intel ricoh_mmc psmouse pcspkr led_class nvidia(P) lbm_cw_mac80211 lbm_cw_cfg80211 i2c_core snd_pcm_oss snd_mixer_oss snd_pcm snd_seq_dummy snd_seq_oss snd_seq_midi snd_rawmidi snd_seq_midi_event snd_seq snd_timer snd_seq_device video output battery snd soundcore wmi intel_agp ac button snd_page_alloc shpchp pci_hotplug ext3 jbd mbcache sd_mod crc_t10dif sr_mod cdrom sg ata_generic pata_acpi usbhid hid ata_piix ahci libata scsi_mod dock ohci1394 tg3 ieee1394 libphy ehci_hcd uhci_hcd usbcore thermal processor fan fbcon tileblit font bitblit softcursor fuse
[  208.616836] Pid: 6638, comm: iwconfig Tainted: P        W 2.6.27-10-generic #1                                       
[  208.616841]                                                                                                          
[  208.616842] Call Trace:                                                                                              
[  208.616857]  [<ffffffff8024e9b4>] warn_on_slowpath+0x64/0x90                                                         
[  208.616881]  [<ffffffffa0b85e06>] ? iwl_radio_kill_sw_enable_radio+0x16/0x180 [iwlcore]                              
[  208.616892]  [<ffffffff80501899>] ? mutex_unlock+0x9/0x20                                                            
[  208.616908]  [<ffffffffa0bda00a>] ? iwl_mac_config+0x6a/0x300 [iwlagn]                                               
[  208.616932]  [<ffffffffa02f841c>] ieee80211_hw_config+0xac/0xb0 [lbm_cw_mac80211]                                    
[  208.616961]  [<ffffffffa030fe4d>] ieee80211_set_freq+0x8d/0x90 [lbm_cw_mac80211]                                     
[  208.616985]  [<ffffffffa02f90cf>] ieee80211_ioctl_siwfreq+0x7f/0x100 [lbm_cw_mac80211]                               
[  208.616995]  [<ffffffff804eae16>] ioctl_standard_call+0x66/0xf0                                                      
[  208.617002]  [<ffffffff804eadb0>] ? ioctl_standard_call+0x0/0xf0                                                     
[  208.617014]  [<ffffffff804ea9b0>] ? ioctl_private_call+0x0/0xb0                                                      
[  208.617021]  [<ffffffff804eb030>] wireless_process_ioctl+0xe0/0x170                                                  
[  208.617028]  [<ffffffff804ea9b0>] ? ioctl_private_call+0x0/0xb0                                                      
[  208.617035]  [<ffffffff804eadb0>] ? ioctl_standard_call+0x0/0xf0                                                     
[  208.617041]  [<ffffffff804eb12f>] wext_ioctl_dispatch+0x6f/0xb0
[  208.617049]  [<ffffffff804eb286>] wext_handle_ioctl+0x46/0x90
[  208.617057]  [<ffffffff8046725f>] dev_ioctl+0x3cf/0x410
[  208.617065]  [<ffffffff8026b51e>] ? up_read+0xe/0x10
[  208.617072]  [<ffffffff80505b52>] ? do_page_fault+0x372/0x750
[  208.617080]  [<ffffffff80455631>] sock_ioctl+0x91/0x280
[  208.617087]  [<ffffffff802f8926>] vfs_ioctl+0x36/0xb0
[  208.617093]  [<ffffffff802f8c23>] do_vfs_ioctl+0x283/0x2f0
[  208.617099]  [<ffffffff802f8d31>] sys_ioctl+0xa1/0xb0
[  208.617109]  [<ffffffff8021285a>] system_call_fastpath+0x16/0x1b
[  208.617113]
[  208.617116] ---[ end trace 47d2c4b7c5ff0fd5 ]---
[  208.640198] iwlagn: index 0 already used in uCode key table.
[  208.640208] iwlagn: No space for Tx
[  208.640213] iwlagn: Error sending REPLY_WEPKEY: enqueue_hcmd failed: -28
[  212.333467] iwlagn 0000:06:00.0: PCI INT A disabled
[  214.230310] tg3: eth0: Link is up at 100 Mbps, full duplex.
[  214.230322] tg3: eth0: Flow control is on for TX and on for RX.
[  218.147585] iwlagn 0000:06:00.0: PCI INT A -> GSI 19 (level, low) -> IRQ 19
[  218.147742] iwlagn 0000:06:00.0: restoring config space at offset 0x1 (was 0x100002, writing 0x100006)
[  218.352563] Registered led device: iwl-phy0:radio
[  218.352608] Registered led device: iwl-phy0:assoc
[  218.352645] Registered led device: iwl-phy0:RX
[  218.352692] Registered led device: iwl-phy0:TX
[  218.388043] iwlagn: index 0 already used in uCode key table.
[  227.854287] NET: Registered protocol family 10
[  227.855347] lo: Disabled Privacy Extensions
[  227.858277] ADDRCONF(NETDEV_UP): wlan0: link is not ready



Other info:

[  293.987690] wlan0: direct probe to AP XX:XX:4b:15:a5:a0 try 1
[  294.000676] wlan0: direct probe to AP XX:XX:4b:15:a5:a0 try 1
[  294.000711] wlan0 direct probe responded
[  294.000718] wlan0: authenticate with AP XX:XX:4b:15:a5:a0
[  294.004527] wlan0: authenticated
[  294.004538] wlan0: associate with AP XX:XX:4b:15:a5:a0
[  294.006809] wlan0: RX AssocResp from XX:XX:4b:15:a5:a0 (capab=0x411 status=0 aid=3)
[  294.006818] wlan0: associated
[  294.027795] wlan0: disassociating by local choice (reason=3)
[  296.024258] wlan0: privacy configuration mismatch and mixed-cell disabled - disassociate
[  307.568164] CE: hpet increasing min_delta_ns to 15000 nsec


[  512.564765] iwlagn: Radio Frequency Kill Switch is On:
[  512.564770] Kill switch must be turned off for wireless networking to work.
[  517.300243] wlan0: no IPv6 routers present
[  522.202037] Registered led device: iwl-phy0:radio
[  522.203729] Registered led device: iwl-phy0:assoc
[  522.205532] Registered led device: iwl-phy0:RX
[  522.207168] Registered led device: iwl-phy0:TX
[  522.207479] iwlagn: TX Power requested while scanning!


The scan work:
the wireless find the ap but disassociate.
In iwconfig ap is not present.


I have compiled and installed compat-wireless-2008-12-11
but i have same problem (but the scan work)

[  408.182065] wlan0: disassociating by local choice (reason=3)
[  408.205276] iwlagn: index 0 not used in uCode key table.
[  410.176396] wlan0: privacy configuration mismatch and mixed-cell disabled - disassociate
[  418.188105] wlan0: no IPv6 routers present