so , tell me why my blog not displaying skysraper (both side right and left panal) ad ? gape between (friends and My friends at the left panal ) you can check in my sig systemctc tell me why www.systemctc.blogspot.com
First, read ADsense TOS again. Second, try to add one ad unit only and make sure that that the space on your sidebar is enough for the size of the skyscraper.
You should not more than three ads in any webpage. You can place 3 textual and 3 link ads in the same page. But don't put more ads at the same place. It won't look professional and your visitors won't stay more time in your website. Try to keep ads in professional way.