Hi Rogurt, here are a few previous discussion topics where there was some troubleshooting done for filleting, not sure if any of these have to do with your particular cases though:

http://moi3d.com/forum/index.php?webtag=MOI&msg=4475.6
http://moi3d.com/forum/index.php?webtag=MOI&msg=4321.2
http://moi3d.com/forum/index.php?webtag=MOI&msg=4192.1
http://moi3d.com/forum/index.php?webtag=MOI&msg=3829.1
http://moi3d.com/forum/index.php?webtag=MOI&msg=4712.1


Those may give you some ideas, but really the primary way to troubleshoot a particular problem is to post the model file here in the forum.

- Michael