That's a good one Sherif,,, It looks like there is an issue where your 3DSketch2 crosses over the mirror line that is causing a problem with this. Not sure how to fix that at the moment but I noticed that if I added some lines that straddle the mirror edge then split your sketch it works. Might have to add another operation in order to trim those areas. Or since it looks like you want this symmetrical perhaps you can make your trim prior to the mirror??