Isn't the man LWP::Simple man page quite clear what it does? Quoting said man page:

  head($url)
     Get document headers. Returns the following 5 values if successful:
     ($content_type, $document_length, $modified_time, $expires, $server)

     Returns an empty list if it fails.  In scalar context returns TRUE
     if successful.

Perhaps none of those headers are actually send by your works server.

Or perhaps your server doesn't respond nicely to HEAD request. Telnet to its port, issue an proper HEAD request, and see what it returns.