Comment 3 for bug 1496229

I think I had a similar issue, "continue" button was grayed out in the installer on the "installation type" screen. The steps I used were:
* Boot from USB drive with 15.10 beta 2
* Click through the install, get to installation type (erase full disk / install alongside question). No popups / unusual questions so far.
* "Continue" button is disabled regardless of option chosen

Going back in the wizard, then forward again, let me continue further. This was on a machine with an existing Windows install, if that matters