title: Invalid file name error in Eclipse
body: <p>I often encounter the following error:</p>
  
  <blockquote>
    <p>res\drawable\my-image-48.png: Invalid file name: must contain only [a-z0-9_.]</p>
  </blockquote>
  
  <p>My file name is "my-image-48.png" which seems to conform to the constraints listed in the error. </p>
  
  <p>What am I missing?</p>