Rails - Aug 2006 - Problems installing Subscript

Has any one installed subscript engine. I having trouble completing the 
installation: When I run
rake db:migrate:engines:substruct I get the following error;

(in /Users/peterw/railsapps/webprint)
Migrating engine ''substruct''
== AddUserAndContact: migrating 
==============================================-- add_column(:questions,
:email_address, :string, {:limit=>50})
   -> 0.1110s
-- change_column(:questions, :answered_on, :datetime, {:null=>true})
rake aborted!
Mysql::Error: Invalid default value for ''answered_on'': ALTER
TABLE
questions CHANGE answered_on answered_on datetime DEFAULT ''''

Thanks