Looks like the table did not get dropped. Either the down action in the Migration did not include the drop command or the command rake db:migrate VERSION=6 did not succeed. To resolve the issue you need to take one of the following steps:
rake db:reset #Only works in Edge or w/ Sake
drop your database, recreate it and remigrate
drop the specific table that was causing the problem either from the command line or from a gui client.
add :force => true to your migrations table create line (think carefully before doing this one)