title: setResourceValue NSURLTagNamesKey error
body: <p>I am getting an error when trying to set a tag color Blue to a file using setResourceValue:</p>
  
  <pre><code>var error: NSError?
  let listofTags = NSWorkspace.sharedWorkspace().fileLabels
  let theURL:NSURL = NSURL.fileURLWithPath("/Volumes/234567_fr.tif")!
  
  var Tag: AnyObject = NSWorkspace.sharedWorkspace().fileLabels[4] // Tag = "Blue"
  
  theURL.setResourceValue(Tag, forKey: NSURLTagNamesKey, error: &amp;error)
  println(error) // Error Domain=NSOSStatusErrorDomain Code=-8050 "The operation couldn’t be completed. (OSStatus error -8050.)
  </code></pre>
  
  <p>Any idea? Thank you for your help</p>