Ubuntu 13 server network install fails at "Install the system"--

Hi!

I'm doing an install from ubuntu-13.04-server-amd64.iso with PXE boot and http mirror. However, it fails at the "Install the system step". I've tried this from VMWare (both server and client) and in real machines (again, both real machines in a LAN), so it's not likely to be a HW issue. Any suggestions?

Setup:
* DHCP, TFTP with dnsmasq. Serves the netinstall ISO for Ubuntu 13
* Apache2 servs the contents of ubuntu-13.04-server-amd64.iso thru the network
* Expert install
* Client machine boots up from network, detects the mirror, downloads installation packets perfectly, and then, at the "Install the system", fails with this message:
"An installation step failed. You can try to run the failing item again from the menu, or skip it and choose something else. The failing step is: Install the system"
* Going to the virtual console 4, I get:
INFO: Menu item 'live-installer' selected --> Notice I selected "normal", not "live"
error: Could not find any live images
WARNING **: Configuring 'live-installer' failed with error code 1
WARNING **: Menu item 'live-installer' failed.
kernel: [140.294528] sda6: WRITE SAME failed. Manually zeroing.


In the same setup, the Debain 7 install works.
Thank you a lot!