I was getting the strangest dialog box when trying to Save As... an .htc file in VS.NET -- something to do with checking out a file modified in memory...? Anyway, I finally realized that I was editing the .htc file with the frightening VS.NET HTML/XML editor! <gasp>
So I quickly changed the default editor for .htc files to the Source Code Editor with Open With... in the Solution Explorer, as I'd already done for .html, .xml, and .js files.
One of these days I'm going to post all of my favorite settings for all of my favorite software programs. Really!