Fruits have calories, they also have sugar, carbs, etc...just like all other foods. Just because Weight Watchers tells you they are 0 points, doesn't mean it's 0 everything else.
The Points Plus program is designed for you not to have to count fruits, however, it's not designed for you to go into fruit overload. Remember the guidelines say you should have 5 servings of fruits or vegetables daily, the program is designed to accomodate that. Sure, you can have more..but if you're finding your weight has stalled or the program just isn't working for you, before hopping back to the old program or quitting all together, look to see what is going on.
Weight Watchers is a business so it's not going to offer the advice I'm going to give you because it would be promoting some competition...but you should spend a week or two at one of the calorie counting sites. Log your menus in there and get a look at what you are consuming in a day! SparkPeople is a nice FREE site that will show you your calorie intake, carb intake, etc. It could be an eye opening experience.
And don't go into fruit overload 0 points, doesn't mean 0 calories!!