Sorry to resurrect an old
thread...
If you have a SelectManyListbox, and you want to remove one or multiple selectItems, another option is to use a nested for loop.
As you know a SelectManyListbox uses a List for the SelectItems and possibly a
String array (or collection or map) for the values in the listbox.
The outer for loop would be the length of the selected items in the list box, the inner for loop would be the size of the items in the listbox. Match the inner loop value to the outer loop value and remove the inner loop value at the inner loop index. (clear as mud, right?).