"Overly complex wall surfaces being produced. One or more walls may have a large amount of openings or complex mulled units. Try simplifying the openings in the wall or using the wall break tool."
There is a wall in your plan that contains a lot of openings, a complex set of openings, or there is a large number of mulled openings in one wall.
In order to resolve this issue, you must first locate the wall in question. Some things to look for when attempting to locate the problem wall are:
A really long wall that has a lot of openings in it. Openings include doors, windows and masonry fireplaces.
A wall with a large number of complex openings such has non-rectangular windows.
A wall that has multiple mulled openings in it.
To resolve this issue after the problem wall has been found
If you have a wall that has multiple mulled openings in it:
Select each mulled unit and click the Open Object edit button.
On the Options panel of the Mulled Window Specification dialog, check the box beside Single wall hole and click OK.
In all cases, a solution that will work is to use the Break Wall tool to break the single wall up into more than one wall. This will result in less surfaces being created on one wall.
Select Build> Wall> Break Wall from the menu, then click along the problem wall to place a break at that location.
You will not be able to place a break in a location where an opening already exists, so place the break on either side of an opening in the wall. The point where an interior wall intersects the problem wall is sometimes a good place to position a break.