ERROR: volatile EquivalenceClass has no sortref

When am trying to query a table temp_table1(sms_type varchar(20),sms_info varchar(100),sms_id integer) 

Query :: select sms_type,count(*) from  temp_table1 group by 1 order by 2 desc;

Then i got following errors , i dont know whats wrong in this .

This is my first post to forum , Please suggest me if i miss something .
--
--Regards
  Ranjeet  R. Dhumal