getting random error while upload photo with paper

问题:

I used gem "paperclip" for upload images and gem "paperclip-storage-ftp" for store images on my own ftp server. It worked fine for a while, but now I am getting random errors, when I upload photos.

Sometimes this

Net::FTPReplyError - 150 Connecting to port 3270

Sometime this

Net::ReadTimeout - Net::ReadTimeout:

Sometime this

Paperclip::Storage::Ftp::NoServerAvailable

.. and sometimes this:

Net::FTPPermError - 500 ?

Model

class AlbumPhoto < ActiveRecord::Base
  has_attached_file :photo, {
    # Choose the FTP storage backend
    :storage => :ftp,
    :path => "www.abcd.com/:attachment/:id/:style/:filename",
    :url => "ftp://[e-mail]@domain.com/www.abcd.com/:attachment/:id/:style/:filename",

    :ftp_servers => [
      {
        :host => "domain.com",
        :user => "[e-mail]",
        :password => "abcd123",
        :passive => true
      }
    ],
    :styles => { :medium => "300x300^", :thumb => "100x100^" ,:large => "400x400^"},

  }  
end

Why is this happening?