I tried to download that free log cabin pattern, too, from the knit-o-matic website that is accessible from Ravelry...but both of my download attempts were unsuccessful. There is something wrong with their software or their website itself IMO.
I learned the fundamentals of log cabinning from the Mason-Dixon book. You can find a log cabin project page at Ravelry by typing Mason-Dixon log cabin into the pattern search. They offer a free log cabin pattern, the Moderne Baby Log Cabin. I've knit that one several times.
But if you want to learn the other log cabin style like my black-red-grey-cream blanket, you might have to buy the book from Amazon, and a link for the book is on the Mason-Dixon log cabin project page at Ravelry. Or maybe your local library has one in stock.
BTW, the book is worth every dollar! It's their best book ever!