ERROR:HDLParsers:812 A Value is missing in case

If you get the following error:

ERROR:HDLParsers:812 - "file_name" Line ###. A value is missing in case.

The first reason is covered by the AR record http://www.xilinx.com/support/answers/14430.htm

This just means you forgot to add when others => to your case statement. The other way to solve this is really freaking weird but I ran into this in ISE 13.2

 when "11" =>      
      TOKEN<= "0000";                
    --synthesis translate_off
    when others =>
      null;
    --synthesis translate_on

Also caused this error, unbelievably just moving the commends down after the when others solves it

 when "11" =>      
      TOKEN<= "0000";                
 when others =>
      null;
     --synthesis translate_off
    --synthesis translate_on