problems uploading .zip files with attachment_fu

I'm using attachment_fu for uploading all of my files and have done so
successfully except when I try to upload zip files.

I continuously get this error: "Size is not included in the list"

I implemented this fix: http://www.railsforum.com/viewtopic.php?id=6307

but it didn't work.

Here is my model code:

  has_attachment :content_type => 'application/zip',
                 :storage => :file_system,
                 :path_prefix => '../downloads',
                 :max_size => 11102400.kilobytes,
                 :min_size => 2.kilobytes

  validates_as_attachment