marmoset toolbag 1.06 rendering issue

Giankharlo

Hello guys , Im using marmoset to render a sinple piece as you can see in the attached image but Im having a problem when exporting the mesh to marmoset after softening the edges , a small part of the mesh turns black!!!when hardening edges problem goes away , but I dont like of the gun with an squarish cylinder , but in maya looks ok , no flipped normal ,diffuse, normal, spec already checked they are ok , so please if anyone knows whats going on drop me a line , thanks in advance guys and have a good day !!!!