lost swap after installing mainline kernel (requested for debugging)

After reporting Bug #681016 I was asked to install a mainline kernel to see if the problem was still present. This caused me to lose swap (swap is disabled, and swapon -a gives an error).

> sudo swapon -a
swapon: /dev/sda7: read swap header failed: Invalid argument

This problem persists even after uninstalling the new kernel and booting the old one.

ProblemType: Bug
DistroRelease: Ubuntu 10.10
Package: linux-image-2.6.35-22-generic 2.6.35-22.33
Regression: Yes
Reproducible: No
ProcVersionSignature: Ubuntu 2.6.35-22.33-generic 2.6.35.4
Uname: Linux 2.6.35-22-generic x86_64
NonfreeKernelModules: wl
AlsaVersion: Advanced Linux Sound Architecture Driver Version 1.0.23.
AplayDevices:
 **** List of PLAYBACK Hardware Devices ****
 card 0: Intel [HDA Intel], device 0: ALC268 Analog [ALC268 Analog]
   Subdevices: 1/1
   Subdevice #0: subdevice #0
Architecture: amd64
ArecordDevices:
 **** List of CAPTURE Hardware Devices ****
 card 0: Intel [HDA Intel], device 0: ALC268 Analog [ALC268 Analog]
   Subdevices: 1/1
   Subdevice #0: subdevice #0
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC0: trond 1584 F.... pulseaudio
CRDA: Error: [Errno 2] No such file or directory
Card0.Amixer.info:
 Card hw:0 'Intel'/'HDA Intel at 0xf8300000 irq 46'
   Mixer name : 'Realtek ALC268'
   Components : 'HDA:10ec0268,10280275,00100003'
   Controls : 12
   Simple ctrls : 7
Date: Fri Dec 10 11:56:52 2010
Frequency: This has only happened once.
HibernationDevice: RESUME=/dev/sda7
InstallationMedia: Ubuntu 10.10 "Maverick Meerkat" - Release Candidate amd64 (20100928)
MachineType: Dell Inc. Vostro1710
ProcCmdLine: BOOT_IMAGE=/boot/vmlinuz-2.6.35-22-generic root=UUID=d38e9c68-1752-4dd8-92d0-59d48e3946a0 ro quiet splash
ProcEnviron:
 LANGUAGE=en
 PATH=(custom, user)
 LANG=en_GB.utf8
 SHELL=/bin/bash
RelatedPackageVersions: linux-firmware 1.38
RfKill:
 0: dell-wifi: Wireless LAN
  Soft blocked: no
  Hard blocked: no
SourcePackage: linux
WifiSyslog:

dmi.bios.date: 10/09/2008
dmi.bios.vendor: Dell Inc.
dmi.bios.version: A10
dmi.board.name: 0X805C
dmi.board.vendor: Dell Inc.
dmi.chassis.type: 8
dmi.chassis.vendor: Dell Inc.
dmi.chassis.version: N/A
dmi.modalias: dmi:bvnDellInc.:bvrA10:bd10/09/2008:svnDellInc.:pnVostro1710:pvrNull:rvnDellInc.:rn0X805C:rvr:cvnDellInc.:ct8:cvrN/A:
dmi.product.name: Vostro1710
dmi.product.version: Null
dmi.sys.vendor: Dell Inc.