Guest Pass Acceptance or Activation Failure

http://support.steampowered.com/cgi-bin/steampowered.cfg/php/enduser/std_adp.php?p_faqid=550

This issue occurs when a connection to the Steam Guest Pass servers cannot be established.

Please exit and restart Steam to begin troubleshooting this issue. If the issue persists after you have reconnected, please see the Game Errors: Secure connection failed, No Steam logon, or A connection to the VAC servers could not be made FAQ for further troubleshooting instructions.