I have the problem like it before. What I do is :
1. Re-install Gem
2. do script/mailer again, but do not replace model
3. restart my server
4. Back working 
Enjoy, Reinhart {$_$} http://teapoci.blogspot.com
I have the problem like it before. What I do is :
1. Re-install Gem
2. do script/mailer again, but do not replace model
3. restart my server
4. Back working
Enjoy, Reinhart {$_$} http://teapoci.blogspot.com