The 10.04 LiveCD with LinuxCNC 2.5 had a small issue that might have affected a few people when installing and this has been corrected. If your installing LinuxCNC make sure your iso file is
ubuntu-10.04-linuxcnc3-i386.iso (note the 3 after linuxcnc is the latest one).
If you installed from the LiveCD using
ubuntu-10.04-linuxcnc2-i386.iso in order to get updates you will have to open the Synaptic Package Manager and go to Settings > Repositories > Other Software tab and change the edit the EMC entry's to reflect the re-branding change as shown below.
John