In a decision on October 24, the Brussels Court of First Instance accepted ISP Scarlets argument that the filter, called Audible Magic, did not work.
The decision is a defeat for the music copyright collecting society SABAM.
Last year, SABAM won a case in the same court against Scarlet, arguing that the ISP was liable for copyright infringement carried out by its users.
The judge ordered that Scarlet should use the filtering technology to stop the copying and gave the company six months to comply.
Scarlet was also ordered to pay 2,500 a day as long as the illegal file sharing continued.
But the judge has now ruled that it does not need to pay the fines, which have added up to some 750,000.
The technical and legal issues raised in the case will now be heard in full by the Brussels Court of Appeal in October next year.