I think I'm starting to understand and had no idea that by simply having a forum post title that was similar to my article this would occur.
Thank you for the tip.
Would this have had such an effect on rankings though? This is just one page that was hurt - the rest haven't been posted anywhere and they dropped off the face of the earth too. I had a number of other key words and phrases that contributed to the 600 impressions per day down to 10.