See the Rapture post at
http://forum.cakewalk.com/tm.aspx?m=2667101&mpage=4. Ryan from Cakewalk is working on this and has gotten to the bottom of what's happening, but, as of late yesterday night, needed to get someone else from Cakewalk to look into a fix, but it was Saturday night in Boston...
The gist of the issue is that whether it installs for you or not depends on what version of Dimension Pro you had installed prior to the X2 Producer installation (for some reason the Rapture installer is checking for prior versions of Dimension rather than prior versions of Rapture).
Late in the thread at the link, lorneyb2 posted a workaround for installing Rapture that someone marked as being helpful (so it will stand out when you scan the page). That fix didn't work as is for me, but I posted some additional notes about 8 posts down from there with the additional things I did to get it to work for me. While we both did it with a separate Rapture installer that was posted yesterday (it isn't there anymore as it didn't solve the problem by itself), it should also work by using the X2 Producer installer and just selecting Rapture as what to install. The catch, though, is that you have to be willing to do a bit of registry hacking to get it to work, renaming one or two keys before the Rapture installation then renaming them back to their old names afterward. (Basically the workaround tricks the Rapture installer into thinking you don't have Dimension Pro on your system.)
Rick