One thing that comes to mind from looking at your image is it looks as though the profile might have been placed very near but not on a vertex of the circular path. This would result in a very short section of extrusion between the profile and the vertex where the extrusion changes direction. And that short section would result in a gap. The best thing to do would be to place the the profile at the mid point of a side of the circle to get equally long sections of extrusion on either side of the profile. Of course if the side of the circle is extremely short you'll still have issues. Second best would be to place the profile at the vertex itself. The downside, although it may not matter much in this case is that the resulting extrusion will be distorted a bit relative to the original profile.