Undefined method issue in file_column temp object

Hi All,
      I'm using file_column_field for uploading the images it's working
fine.But it throws random error as shown below.
           eg.,
              <%= file_column_field("ad","ad_picture")%>
              I'm using like this,but while uploading or editing the
image it throws an error randomly:
                 undefined method : ad_picture_temp for<Ad:#Object>
          i think this issue is comes while creating the file column
temporary(temp) object.
          It occurs randomly.In single port its working fine,but i
configured in multiple port but it throws an error randomly.
          Can someone please help on this?
          Thanks in Advance..
Regards,
Viswanathan.J