title: R cannot melt data.frame
body: <p>I have the following data.frame, called tableMS:</p>
  
  <pre><code>     X   Y        Z        T
  1  375 855 455.7259 3777.856
  2  395 969 347.8306   2506.7
  3  449 811 309.9512 519.8513
  4  451 774  278.291 717.8705
  5  453 774  278.291 717.8705
  6  455 774  278.291 717.8705
  7  521 697  376.734 693.8541
  8  529 855 455.7259 3777.856
  9  531 855 455.7259 3777.856
  10 609 774  278.291 717.8705
  </code></pre>
  
  <p>when I try to use the function melt()</p>
  
  <pre><code>MeltTable &lt;- melt(tableMS,id=c("X","Y"))
  </code></pre>
  
  <p>I get the following error:</p>
  
  <pre><code>Error in match.names(clabs, names(xi)) : 
     names do not match previous names
  </code></pre>
  
  <p>I struggle to understand what happens, any idea?</p>
  
  <p>Edit:
  I generated tableMS as portion of a bigger table and the output of str(tableMS) is:</p>
  
  <pre><code>'data.frame':   10 obs. of  4 variables:
  $ X: num  375 395 449 451 453 455 521 529 531 609
  $ Y: num  855 969 811 774 774 774 697 855 855 774
  $ Z:List of 10
    ..$ : num 456
    ..$ : num 348
    ..$ : num 310
    ..$ : num 278
    ..$ : num 278
    ..$ : num 278
    ..$ : num 377
    ..$ : num 456
    ..$ : num 456
    ..$ : num 278
  $ T:List of 10
    ..$ : num 3778
    ..$ : num 2507
    ..$ : num 520
    ..$ : num 718
    ..$ : num 718
    ..$ : num 718
    ..$ : num 694
    ..$ : num 3778
    ..$ : num 3778
    ..$ : num 718
  </code></pre>