[Rails] Can't dump File ... when uploading files

I am getting this error on the redirect_to command ...

I am using Rails 3 w Paperclip to upload files ( but I tried also
CarrierWave .. same error)
I tried to change the session store from cookie-based to database ..
same error
I tried to delete the params content ...
I don't know what to try next .. any clue ?

thanks

erwin

--
You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group.
To post to this group, send email to rubyonrails-talk@googlegroups.com.
To unsubscribe from this group, send email to rubyonrails-talk+unsubscribe@googlegroups.com.
For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en.