Error "additional plane required" when trying to convert an outline block to building block

The message 'additional plane required' can be generated following a cut operation and subsequent attempt to convert to a building block when DesignBuilder is unable to generate the required geometry. This is caused by the outline block having a geometry such that a vertex on the outline block is adjacent to 4 or more surfaces. The algorithm used by DesignBuilder to generate blocks from outlines cannot deal with this situation. DesignBuilder developers will be adding a new block type with 'paper thin walls' that is more flexible and allows almost all geometries and this should be available with v3 in 2011.

In the meantime, it is usually possible to simplify the blocks in such a way that this problem does not arise. This may involve using more smaller blocks or simplifying a larger block.