3/4 column layout doesn't work

Hi again,
The shortcode for the 3/4 column layout doesn’t work:
the fourth_col_right is there (slightly below), but the three_fourth_col
does’nt appear…
It seems that there’s no place enough or the three_fourth_col class doesn’t exist.
Another thing:
I tried to integrate a widget into this layout but it doesn’t work even if i use hierarchical mode and good widget ids like “sidebar”, “leftsidebar”, etc…