It should be
code:
while(PlusWnd.LstView_GetCount("ListView") != 0)
This will give a boolean expression like the while statement wants
This method I have found works well, I have used it before with Message Customizer! Live when I did the groups to clear out the list views. However, seeing as though Mattike uses windows API it might be quicker and nicer to use that (especially on larger lists).