Problem to create thumbnails with Attachment FU + ImageScience

Hello

I have a problem in the creation of a thumbnail for an uploaded image
(with Attachment Fu)
For resizing images, i've installed ImageScience, following steps of
this article (on Mac 10.4.0 : freeimage installed with MacPort,
ImageScience 1.1.3 gem installed (aith its dependencies), AttachmentFu
plugin installed)

When resizing the image, i get the following error stack at the screen
(and all messages of validations for my model class)

/usr/local/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/
active_record/validations.rb:764:in `save_without_transactions!'
/usr/local/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/
active_record/transactions.rb:133:in `save!'
/usr/local/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/
active_record/connection_adapters/abstract/database_statements.rb:
59:in `transaction'
/usr/local/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/
active_record/transactions.rb:95:in `transaction'
/usr/local/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/
active_record/transactions.rb:121:in `transaction'
/usr/local/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/
active_record/transactions.rb:133:in `save!'
vendor/plugins/attachment_fu/lib/technoweenie/attachment_fu.rb:215:in
`create_or_update_thumbnail'
/usr/local/lib/ruby/gems/1.8/gems/activesupport-1.4.2/lib/
active_support/core_ext/object/misc.rb:23:in `returning'
vendor/plugins/attachment_fu/lib/technoweenie/attachment_fu.rb:207:in
`create_or_update_thumbnail'
vendor/plugins/attachment_fu/lib/technoweenie/attachment_fu.rb:367:in
`after_process_attachment'
vendor/plugins/attachment_fu/lib/technoweenie/attachment_fu.rb:367:in
`each'
vendor/plugins/attachment_fu/lib/technoweenie/attachment_fu.rb:367:in
`after_process_attachment'
/usr/local/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/
active_record/callbacks.rb:333:in `send'
/usr/local/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/
active_record/callbacks.rb:333:in `callback'
/usr/local/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/
active_record/callbacks.rb:330:in `each'
/usr/local/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/
active_record/callbacks.rb:330:in `callback'
/usr/local/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/
active_record/callbacks.rb:243:in `create_or_update'
/usr/local/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/
active_record/base.rb:1545:in `save_without_validation'
/usr/local/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/
active_record/validations.rb:752:in `save_without_transactions'
/usr/local/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/
active_record/transactions.rb:129:in `save'
/usr/local/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/
active_record/connection_adapters/abstract/database_statements.rb:
59:in `transaction'
/usr/local/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/
active_record/transactions.rb:95:in `transaction'
/usr/local/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/
active_record/transactions.rb:121:in `transaction'
/usr/local/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/
active_record/transactions.rb:129:in `save'
app/controllers/player_controller.rb:35:in `signup'

Has anyone already encountered this kind of error?

Regards

Laurent

The article is http://clarkware.com/cgi/blosxom/2007/02/24
Mac OS X 10.4.10

Laurent