Comment 23 for bug 294667

Sorry, my previous comment is nonsense. If you want to circumvent the problem, do one of:

1] If you don't need the backports module, remove it.

2] If you do need the backports module, either:

 2a] Downgrade your kernel image package to 2.6.27-7, install version 2.6.27-7.4 of the backports,
     and pin the version of these packages in Synaptic (Package > Fix Version).

 2b] If you really want to stick to kernel 2.6.27-8, install version 2.6.27-7.4 of the
     linux-backports-modules-2.6.27-7-generic package, pin it in Synaptic, and also install package
     linux-backports-modules-intrepid, which will install version 2.6.27-8.7 of the backports. Then on
     a terminal type:
     1$ cd /lib/modules/2.6.27-8-generic/
     2$ sudo mv updates backup_updates
     3$ sudo ln -s ../2.6.27-7-generic/updates
     which effectively replaces one with the other so that Ubuntu "believes" it's using 2.6.27-8 but actually
     it's using 2.6.27-7. It's ugly, yes.
     Then reboot your computer and you should have stable wireless again. Chances are this may not work
     if another backported module is in use which clashes with the ABI of 2.6.27-8, but iwl3945 seems OK
     about this -- the module has certainly loaded, I'm using it at the moment.

     If kernel 2.6.27-9 is released without solving this issue you may need to repeat the commands
     above, replacing the "8" in step 1 with a "9". But I certainly hope it is solved by then.

Hope this helps.