Lenovo X200T cannot suspend or hibernate

The laptop doesn't get to sleep anymore, but it did around 3 months ago, so it might be a kernel-related bug. Here is the syslog extract after running "sudo pm-suspend":

Oct 14 11:01:33 cherry kernel: [ 3387.516767] Freezing user space processes ... (elapsed 0.01 seconds) done.
Oct 14 11:01:33 cherry kernel: [ 3387.532119] Freezing remaining freezable tasks ... (elapsed 0.01 seconds) done.
Oct 14 11:01:33 cherry kernel: [ 3387.548124] PM: Entering mem sleep
Oct 14 11:01:33 cherry kernel: [ 3387.548216] Suspending console(s) (use no_console_suspend to debug)
Oct 14 11:01:33 cherry kernel: [ 3387.550699] sd 2:0:0:0: [sda] Synchronizing SCSI cache
Oct 14 11:01:33 cherry kernel: [ 3387.552484] sd 2:0:0:0: [sda] Stopping disk
Oct 14 11:01:33 cherry kernel: [ 3387.600155] legacy_suspend(): pnp_bus_suspend+0x0/0xa0 returns 28
Oct 14 11:01:33 cherry kernel: [ 3387.600160] PM: Device 00:0b failed to suspend: error 28
Oct 14 11:01:33 cherry kernel: [ 3387.665811] PM: suspend of drv:sd dev:2:0:0:0 complete after 115.120 msecs
Oct 14 11:01:33 cherry kernel: [ 3387.665936] PM: Some devices failed to suspend
Oct 14 11:01:33 cherry kernel: [ 3387.670350] sd 2:0:0:0: [sda] Starting disk

The important line here seems to be

Oct 14 11:01:33 cherry kernel: [ 3387.600155] legacy_suspend(): pnp_bus_suspend+0x0/0xa0 returns 28

Thanks!

ProblemType: Bug
DistroRelease: Ubuntu 11.10
Package: pm-utils 1.4.1-8ubuntu1
ProcVersionSignature: Ubuntu 3.0.0-12.20-generic 3.0.4
Uname: Linux 3.0.0-12-generic x86_64
ApportVersion: 1.23-0ubuntu3
Architecture: amd64
Date: Fri Oct 14 10:58:55 2011
EcryptfsInUse: Yes
InstallationMedia: Ubuntu 11.10 "Oneiric Ocelot" - Release amd64 (20111012)
PackageArchitecture: all
SourcePackage: pm-utils
UpgradeStatus: No upgrade log present (probably fresh install)