Failed media upload: “The uploaded file was only partially uploaded.”

I am running Linux CentOS 5.8 and I have my web pages using WordPress 4.0.

I am trying to uplad jpg photos to server via WordPress, but it randomly fails. I uploaded few photos, and then I get errors like:

“4.JPG” has failed to upload due to an error
The uploaded file was only partially uploaded.

Then I try again and again and again until it is successfuly uploaded. Very frustrating.

How can I debug this? Is there a log file? Where to look for?

I solved it by adding

<?php header ("Connection: close"); ?> 

in file.php situated under wp-admin/include