At the Grub screen, highlight but do not click the Install option. Hit the e key.
Scroll down to the line that begins with the word linux, hit the End key to get to the end of the line.
Add a space and
self_update=1
Press F10 to boot the installer and see if that helps. I am not sure if it will, though, in TW.
Note that you will have to wait a few moments while the installer downloads and updates itself. This is only the installer, not the full install DVD, so you are not waiting for a huge download.