ReSharper 6 considers .less files as .CSS, although they aren't.
So instead of proper syntax highlighting, it underlines nearly everything with red (syntax error).
How can I disable this "feature"?
Just found a nice trick:
// /* Disabling ReSharper ;)
// .less code goes here
// */
It's better than disabling ReSharper for a particular set of files (ReSharper -> Options -> Settings -> Edit items to skip ...), since in this case each member of your team doesn't need to repeat this.