title: Missing values in object in R lme
body: <p>I am working on a simple model in R:</p>
  
  <pre><code>fit&lt;-lme(x~y, data, random=~1|subject)
  </code></pre>
  
  <p>But I keep getting this error:</p>
  
  <blockquote>
    <p>Error in na.fail.default(list(h1 = c(103L, 20L, 34L, 85L, 47L, 136L,
    76L,  :    missing values in object</p>
  </blockquote>
  
  <p>(h1 is one of my column titles of a factor)</p>
  
  <p>Any idea on how to fix this? An identical model works with a different set of data.</p>