I never have a problem with.. number 2 when I consume fiber. A lot of times when someone eats too much fiber and has diarrhea or constipation, it means that they aren't drinking enough water.. so drink up! You may have IBS too which can be irritated by too much fiber.
As far as Fiber One Brownies.. I've never tried them, but I know Fiber One products are notorious for containing too much sugar. The 90 calorie one has 8 grams of sugar, which isn't too horrible as an every-now-and-then snack, but not every day (especially if you are consuming a lot of fruits or other foods with sugar).