Error loading photo

When I load the photos I receive this message:

Oops… there seems to be a problem saving the thumbnail, please send the following information to the developer if the problem persists.
WP_Error Object
(
[errors] => Array
(
[invalid_image] => Array
(
[0] => Il file non è una immagine
)
)
[error_data] => Array
(
[invalid_image] => http://xxxxx.altervista.org/xxxxx/wp-content/uploads/2013/12/xxxxx.jpg
)
)

I hope you can help me, thank you very much.

http://ww.wp.xz.cn/plugins/mediaview/