I read somewhere in another thread about the readahead rpm causing this problem. This used to drive me crazy too. Here's what I do:
Run the install normally until I get to the menu where I can select PIAF-Purple, PIAF-Red, etc. I select cancel at the bottom of that menu, then log in to the CLI. Then I typeCode:rpm -e readahead
to get back to the menu.
After that, I can type the three-digit code and my password without any issues. I think it was mentioned in the thread also that the readahead rpm gets uninstalled during the asterisk installation, so it shouldn't cause any problems to uninstall it beforehand.