Many Drupal users got a Notice: Undefined index: #size in file_managed_file_process() (line 446 of .../file.module) error while trying to create/edit a node using the Drupal Multiupload Filefield Widget module. Their files seemed to be uploading correctly but were accompanied by two error messages. If you are getting the same error message under when using the Drupal Multiupload Filefield Widget module then continue reading for the solution.