Upload column - Updating the image using upload_column

I am using upload_column for uploading images. Trying to do the user
registration. For the first time when the user tries to upload image it
works fine. But when try to update the image an error
undefined method `process!' for #<UploadColumn::UploadedFile:0x6838424>
in my view I set the multipart=>true.
and in controller in the edit action @user = User.find(params[:id])
and in update action @user.update_attributes(params[:user]). Do I need
to add anything more?
Please help , thanks in advance