When installing Ubuntu, there is a slide for checking met conditions.
I observed that if you have for example only 384 MB of memory, the installer could crash.
See https://bugs.launchpad.net/bugs/658615 for details.
I'm not sure your particular crash was due to an out of memory situation (though there's one other bug with a similar traceback to yours that's also a suspected OOM), but there's a bug report requesting better dealing with such situations, which Colin Watson (Ubiquity developer) has acknowledged.
See "Meeting Minimum Hardware Requirements" on the Ubuntu documentation for more information on required specs.
I think there is no absolute minimum memory requirement that will work for all circumstances, so it's a bit difficult to check for. I have installed Ubuntu on systems with 256 MiB of RAM, for example.
For example, it depends on what you do in the live environment before you start the installation (or while doing the installation).