Comment 21 for bug 464199

I can confirm this bug - I have the same problem on a new Dell Latitude 6400 Notebook with an Intel 5100 WLAN adapter.
Several other people appear to have this problem as well (see threads:
http://ubuntuforums.org/showthread.php?t=1307396 or
http://ubuntuforums.org/showthread.php?t=1305616 or
http://swiss.ubuntuforums.org/showthread.php?t=1305190 (the proposed solution turning ACPI off, didn't work for me))

I have been running the Karmic beta version on this netbook. Interestingly, WLAN didn't work in the beginning, after some updates it did - for a few days - and then it ceased to work maybe 2-3 days prior to the release candidate (I thought about posting a bug report - I really should have in retrospect... sorry)

The relevant section of "lshw -c network" looks pretty similar

  *-network DISABLED
       description: Wireless interface
       product: Wireless WiFi Link 5100
       vendor: Intel Corporation
       physical id: 0
       bus info: pci@0000:0c:00.0
       logical name: wmaster0
       version: 00
       serial: 00:24:d6:24:47:80
       width: 64 bits
       clock: 33MHz
       capabilities: pm msi pciexpress bus_master cap_list logical ethernet physical wireless
       configuration: broadcast=yes driver=iwlagn latency=0 multicast=yes wireless=IEEE 802.11abgn
       resources: irq:22 memory:f1ffe000-f1ffffff

Hope this helps.