title: Why does Date::Calc complain about "not a valid date"?
body: <p>Previously, this function worked for me...</p>
  
  <pre><code>$this_day = Day_of_Week($lyear, $month, $day);
  </code></pre>
  
  <p>using this lib..</p>
  
  <pre><code>use Date::Calc qw(Add_Delta_Days Day_of_Week Delta_Days);
  </code></pre>
  
  <p>But I need another way to get this same info.</p>
  
  <p>the error it returned is</p>
  
  <pre><code>Date::Calc::Day_of_Week(): not a valid date
  </code></pre>
  
  <p>Any ideas?</p>