Ghassan.
It would be helpful to those who might have an answer if you told us what steps you are taking.
For example step 1 is choosing the corner window tool...2 sleect your window...3 place your cursor on the wall corner etc.
Erika
Architect, Consultant
MacBook Pro Retina, 15-inch Yosemite 2.8 GHz Intel Core i7 16 GB 1600 MHz DDR3
Mac OSX 10.11.1
AC5-18
Onuma System
"Implementing Successful Building Information Modeling"