Hi mrjynx, it's hard to give good feedback just looking at a screenshot alone, could you please also post the 3DM model file along with your screenshot? That then allows things like zooming in and analyzing geometry closely and looking at things from different angles, experimenting with different radius values, etc, etc... none of which can really be done just by looking at a screenshot alone.

One thing that may be a problem is if the 2 surface halves comes to a very shallow (like 2 or 3 degrees) angle to one another. It's a lot more difficult to fillet things that meet in a shallow angle to each other - fillet surfaces only directly touch one another along fully smooth areas, in any kind of crease the fillets do not touch end to end naturally and instead have to be extended, trimmed with one another and have a corner juncture patch put in. When the angle is very shallow these operations become difficult, with things like the corner patches being little teeny tiny slivery things and it becoming difficult to do the intersection between extended fillet pieces because they have more of an overlapping region of intersection rather than a crisp intersection line like you would get at things that meet at a more pronounced angle.

You also might try using the Rebuild command on the arc before doing the Loft or set the option for Profiles : Refit in the Loft command which will probably help to make a single smooth surface as the result of the loft rather than a potentially creased set of 2 surfaces.

- Michael