I'm getting this problem on an Acer Aspire 2920.
I found this in the dmesg output:
[ 25.643400] acerhdf: Acer Aspire One Fan driver, v.0.5.16
[ 25.643405] acerhdf: unknown (unsupported) BIOS version Acer /Aspire 2920 /V1.13 , please report, aborting!
My machine is a 12" Acer Notebook with Core 2 Duo 2GHz CPU rather than an Acer Aspire One with Intel Atom CPU.
I haven't upgraded in a day or so though and I am running an earlier kernel (2.6.31-11-generic) to the one mentioned above. I'm upgrading now so I will report back if the bug is still present.