It could also be that longer processing is already enough. I was doing pralin with a Magimix (which should be roughly equal to your Wearing food processor), and it really took at least 10-15 minutes of processing until the paste was OK. Only to be sure: I used roasted nuts thrown into caramelized sugar, let them cool down, and then put the caramel-nut pieces into the food processor.
If you want to make a nut paste and no pralin, it is very similar. It also takes at least 10 minutes of processing before the nuts properly release their oil. In addtion, the type of nuts used makes a big difference. I would say, the higher the fat content, the easier to make a paste (e.g. Pecan nuts...). Alternatively, it helps to add a little bit of oil to the nuts before or during processing, such as some nut oil or a neutral tasting oil.
However, the earlier comments are all true, you'll never get a perfectly smooth pralin paste or nut paste with a food processor. There will always be a perceivable 'graininess', but for fillings I found it still fairly good and usable!