I will give you some further information about this issue.
This bug seems to affect the powernow-k8 driver in the Ubuntu Versions from 9.10 until 11.04
If I rember correctly Ubuntu 9.04 powernow-k8 was working.
This issue seems to have two main characteristics:
1) Most Atheros WLAN-Adapters stop working with "gain calibration timeout" at dmesg
2) Frequency-Scaling on AMD-Processors stops working at battery-mode -> Its stuck at the lowest frequency
This Bug is reproducable if one boots up with ac device plugged in and plugs off the ac-device.
-> After a short time wlan adaptor stops working and dmesg gives "gain calibration timeout" messages.
The other way round, boot up on battery , plug in ac-device the same bug occures.
There are some "workarounds"
1) The easiest thing is to power down the computer, remove the battery an power up again (Bug occures again from time to time)
2) Another Option is to disable powernow in Bios Settings. (No more WLAN-Bugs, but Frequency-Scaling is not working at battery and ac-mode)
3) Experimental: Some people have managed to get rid of this Bug by using the phc-k8 driver instead of powernow-k8
There is a Ubuntu ppa for this driver att linux-phc.org The driver is mainly used for undervolting modifications.
Look at https://bugs.archlinux.org/task/18982