[Valloric]

I'm out of ideas.

It has to be something with your computer, there are hundreds of people using x64 versions of Sigil without issues (and for 0.1.x, thousands). This thread is the first I've heard of someone being able to run Sigil x86, but not x64.

Let's try eliminating some variables.

1. Uninstall Sigil.
2. Go to Start->Run and type in "regedit" (without the quotes).
3. Find the "HKEY_CURRENT_USER/Software/Strahinja Markovic" folder.
4. Delete it.
5. Download beta3 x64 from the project site.
6. Install it to the default location.
7. Try running it now.

Then report back.