How can you turn schronous scrolling off in Word 2010?

[Muffin]

I'm a writer. I use Word 2010. I want to work on two different Word documents while they're displayed on one screen. I get them side-by-side okay, but I can't work on them separately because they scroll together and my synchronous scrolling button is greyed out so I can't turn it off. I've just spent two hours trying to find a solution without success. The easiest solution would be to turn the synchronous scrolling off, but I can't find a way to do it from the Net. Any help would be appreciated.