Hi Alex,
14.04 LTS is the recommended version. The virtual machine images and iso's for
2.9 and 2.10 all use 14.04.
I bet Mike is correct that you have to use a different config file.
The instructions
http://webwork.maa.org/wiki/Installation_Manual_for_2.8_on_Ubuntu_12.04#Configuring_Apache
call for using webwork.apache2-config.dist
whereas
the instructions
http://webwork.maa.org/wiki/Installation_Manual_for_2.10_on_Ubuntu_14.04#Configuring_Apache
call for using webwork.apache2.4-config.dist
Arnie