The night brings counsel....
Thinking about walls not at 90°.....I checked my project.....the reference wall WAS NOT IN LINE......
So as usual...."for one point...." once I put my initial object back online it no longer gives the transparency error.....
One step forward.. I'll check your suggestions tomorrow.
A detail... since the proportions of the "doors/windows" are blocked, each time you have to re-import the object to adapt it to the width of the wall if you want it flush with both sides of the wall