What is the nature of "one element is completely inside the other?"

[svalen]

I get this error quite often, when flipping walls from inside out,  when adding a new window to an existing wall.

What is the nature of this? Is there a work around? I'm not seeing an element completely in place of another.

Thank you

[barthbradley]

Doesn't sound like window is cutting an Opening in the Wall.  

[barthbradley]

Press "Expand>>" in the Error Dialog Box to find out what elements are conflicting.