if the surfaces are co-planar it's much more efficient to first operate on curves only before making the surfaces. You can use Boolean Region Difference. Works much better, but make sure to define the operation plane for each couple of curves. (eg. using curve panarity analysis component)
Hi, I had a similar problem. Tried everything from creating new curves from the edges to working in construction planes etc. and finally mailed techsupport. Their solution was to set the meshquality to custom. Explanation was that the mesher in Rhino wasn't always as robust as it should be.
hi Tobia Schwinn!
thanks for your comment. i setted the render mesh quality to "smooth & slower" ....nothing changed but set to "custom" it worked ok ^^