title: pandas dt accessor error, column made with to_datetime not datelike?
body: <p>I am confused by an error returned by my Python script:</p>
  
  <pre><code>all_treatments['date'] = pd.to_datetime(all_treatments['INDATUMA'])
  all_treatments['year'] = all_treatments['date'].dt.year
  </code></pre>
  
  <p>The error:</p>
  
  <pre><code>Traceback (most recent call last):
   File "treatments2_noiopro.py", line 93, in &lt;module&gt;
     all_treatments['year'] = all_treatments['date'].dt.year
   File "/home/seidav/anaconda/lib/python2.7/site-packages/pandas/core/generic.py", line 2145, in __getattr__
     return object.__getattribute__(self, name)
   File "/home/seidav/anaconda/lib/python2.7/site-packages/pandas/core/base.py", line 188, in __get__
     return self.construct_accessor(instance)
   File "/home/seidav/anaconda/lib/python2.7/site-packages/pandas/core/series.py", line 2528, in _make_dt_accessor
     raise AttributeError("Can only use .dt accessor with datetimelike "
  AttributeError: Can only use .dt accessor with datetimelike values
  </code></pre>
  
  <p>What am I missing here?</p>
  
  <p>I am using versions pandas 0.16.2 np19py26_0, iopro 1.7.1 np19py27_p0, and python 2.7.10 0 under Linux.</p>