Unable to extrude on some walls

hello,

I’m trying to create a window, but i can’t extrude on the yellow walls. On the green walls there is no problem.

Can you help me ?
plan aide.skp (796.3 KB)

Do you want your yellow wall to be wider at the base (~24 cm) and narrower at the top (20 cm)?

wal-04

If you do, select the face and use Move instead of Push/Pull.