If you've not reduced the syrup enough, it is possible that there will be too much liquid left in the recipe when you are using the food processor. This can be fixed by adding some additional pecans (plain pecans straight from the package will work, or lightly roasted if you have a little time). This should help to thicken the nut butter. Do be aware that nut butters tend to separate a little, so don't be alarmed if it looks a little on the runny side.