Replace <= with < in your for loop. Like this:
for(int i= 0;i<qlist.count();i++)
{
dateStr = qList.at(i).at(6);
}
The reason is qList.count() is the number of items in the list so you do not ever want to try to use qList.at(qlist.count())
Edit: By having <= in the for loop remember that the at last iteration of the for loop i=qlist.count(). So then when the code executes the statement in the loop it essentially does this:
dateStr = qList.at(qList.count()).at(6);