Hi, I came across error while trying to install LyX 2.0.7 in Windows 7 64-bit (actually I have tried in many computers with the same error). I'm using the setup called "LyX-2.0.7-Bundle-1.exe" downloaded from LyX official website. As to Windows, to be exact, I have tried Windows 7 Professional & Enterprise SP1 64-bit but I don't think the *editions* and *SP1* parts are relevant. I think the problem would still happen in other 64-bit Windows O/S, eg XP, Vista, etc.
The error I got are shown in the attached image: the upper dialog appeared first. But almost immediately, it's grayed out and the lower dialog appeared and LyX installation simply was aborted and failed. LyX setup then tried to roll back but it got stuck on "Remove folder: C:\Program Files (x86)\LyX 2.0\" and I had to press the Cancel button. I went a bit further and described here below: I took basic-miktex-2.9.5105.exe and run it in another Windows 7 64-bit and it still crashed! I then downloaded basic-miktex-2.9.5105-x64.exe from MiKTeX official website and tried it but that crashed as well! Seems like MiKTeX setup has very serious problem installing in 64bit O/S! (Off-topic 1: Maybe it's some known bug like http://sourceforge.net/p/miktex/bugs/2208/?) (Off-topic 2: I have heard from some other friends of mine that MiKTeX is actually a big piece of $h!t and their developers, being very arrogant, didn't care about their installer not working in 64-bit O/S and I quite agree with them after finding a lot of mails in their mailing-list which are never answered!) But I found out that if I run basic-miktex-2.9.5105.exe the second time with the option "Reinstall using recommended settings" (which is *only* available when the setup is run outside LyX) after deleting "C:\Program Files (x86)\MiKTeX 2.9" folder, the installation went through the end! Then at this point, if I used "LyX-2.0.7-Installer-1.exe" instead, it's fine. So, it might be nice to warn 64 bit O/S users to download the "LyX-2.0.7-Installer-1.exe" on the download page and give them a little bit help on installing MiKTeX. Hope this helps.