I tried to upgrade Ubuntu 10.04 LTS to 12.04 LTS on my laptop (Fujitsu/Siemens Esprimo Mobile with 2 GB of RAM and an Intel Core 2 Duo Processor). I did it just 2 days ago before the support on Ubuntu 10.04 is expiring, by pressing the upgrade button on the Update Manager's dialog after the most recent update was performed. Everything went well until I needed to reboot. The boot process doesn't continue until after 'Checking battery state... [OK]. There is some intermittent tiny white rectangle in the upper left and the black and white screen and then the process obviously hangs in a loop just producing again and again the same message : [...] iwlagn 0000:08:00.0: Microcode SW error detected. Restarting 0x2000000
Some googling led me to believe it might have to do with the wifi driver which doesn't have the right microcode. So using the pen drive USB linux installer for 12.04 i found out with 'lspci -vnn | grep -i net' that a driver is required for the 'Network Controller Intel PRO/Wireless 4965 AG or AGN [Kedron]' which i found on this website http://wireless.kernel.org/en/users/Drivers/iwlegacyhttp://wireless.kernel.org/en/users/Drivers/iwlegacy Only... exactly this driver (iwlwifi-4965-2.ucode) is already present on /lib/firmware.
Additionally i found out that from the 12.04 install USB pen drive i can start no problem with 'Try Ubuntu' and also the WLAN can be connected. But trying to boot the upgraded system in recovery mode fails with the mentioned error message.
Maybe i should mention that the Ubuntu 10.04 i upgraded from was a Ubuntu server version.
So now i don't know what to do and would appreciate any help from the community.