Hi Guy, can you please post the 3DM model file with your curves in them so I can take a look at your model data?

But yes when the object type reads as a plain "Curve" that means it is open - the start and end points of the curve are not touching. When it reads "Closed crv" that is when it is closed, and in order for Planar to construct a surface the curves you give it need to form a fully closed shape.

There is a plug-in you can get from here:
http://moi3d.com/forum/messages.php?webtag=MOI&msg=2888.11

which can be used to place a point object at the start of an open curve, that can help to show you the area to zoom into to actually see where the gap between the start and end is at.

Normally if you have a closed curve when you mirror it that should also produce a closed curve, so maybe you have run into a bug here, it's hard for me to know for sure without being able to see the actual curves though.

- Michael