rino,

The texture renders fine every time: I tried at least 20 times without any problem.

I suggest you follow Puybarets suggestion:
- move a wall to check that there aren't two walls on top of each other
- if two walls are on top, delete one wall
- if not, move the wall back with Undo
- go to the next wall
- if you find a double wall, make a few renders to check if this solves the problem.

Hans