My chair is not the same in 2.69 and 2.70

Hi all,
I am working on a chair, exporting as COLLADA and looking at it in the GLC-player 3D viewer (OpenGL).
From the very same Blender file, I get different things depending on whether I export from 2.70 or 2.69.
Any explanations ??
Here is the chair in Blender

Exported in GLC from 2.69, it looks fine


But from Blender 2.70, I get these black triangles…


Check for a duplicate mesh hiding in there.
in edit mode, de-select everything, then hover the mouse over the mesh and press L. then move the selected mesh and see if there is a duplicate there.
Also, re-calculate the normals.

Hi Rich,
well I did add a duplicated part under that flat part of the chair. And the original unmodified chair doesn’t show this problem so it looks like you are right.
But until 2.69 I never had problems. Only 2.70 shows this problem
How do I recalculate te normals, by the way. In Edit mode I did ctrl-N but nothing happened (sorry but I have not been playing enough with Blender yet)
Thanks

any modifiers?

ctrl+n recalculates the normals.