Just to say I've installed this locally on my iMac using MAMP and it installed fine so looks like it's something it didn't like on our server. Was a bit annoyed that I wasn't getting to play with it but now I can play locally I'm happy to wait until Beta 2 before trying to install on our server
I experienced the same error. I couldn't click in the button below, because there wasn't any. I waited until xenforo error page was loaded, clicked the back button of my browser and the installation started with the rebuilding again and went through.