[Plugin: NextGEN Gallery] Internal server error

Hi, I get many errors like this one:
“http://www.laidelliwheels.it/wp-content/plugins/nextgen-gallery/xml/media-rss.php?gid=(number)&mode=gallery”
in Google Analytics/Scan errors/Not reachable (I hope the translation is right, I’m using the italian version). How can I manage it? I’m still looking for something that works.
Thank you

http://ww.wp.xz.cn/extend/plugins/nextgen-gallery/