Rmagick image resizing problem

Hi, I am using attachement_fu plugin with Rmagick image processor for uploading images. Even though I am able to upload images properly there is some problem with thubnails created. Thumbs are created with same size as original image. Also the height and width of images are not as null in database. Here is my model.   has_attachment :storage => :file_system,                   :resize_to => '640x480',                   :thumbnails => { :thumb => '160x120', :tiny => '50>' },                   :max_size => 5.megabytes,                   :content_type => :image,                   :processor => 'Rmagick'