Something is obviously wrong with your server. For some reason it's closing the connection. Try to set error reporting to maximum and enable system debugging under Joomla! configuration and try again. But probably it will make no difference.

i did that, but as you said, nothing changed. How do I fix this issue? What shall I ask from my web hosting provider to do?

I doubt that your hosting provider know anything about this. Can you easily transfer the site on a local server and test? What's the server the site is on? ( Apache, Nginx ? ) What's the PHP version of the server?

server api is Apache and pho is 5.3.29

problem solved. web hosting provided switch PHP from 5.3 to 5.4 and Media Manager works perfectly fine now. Many thanks for your instant support

You are welcome.

The only thing I would like to add is that by enabling PHP 5.4 it might have website performance issues and might slow down the website, as per my hosting provider

First, to make things clear, K2 is compatible with PHP 5.3. The specific issue is probably caused by the specific build of PHP. There are several sites with PHP 5.3 where the media manager has no issues.

Regarding the performance usually things get better with new versions. PHP 5.4 is found to be a little slower than PHP 5.3 in some tests however it uses less memory than 5.3.

Finally note that according to the official PHP site the end of life of PHP 5.3 has reached and is recommended that you upgrade to a newer version php.net/archive/2013.php#id2013-07-11-1 .

K2 is probably the best component in Joomla CMS and as I found out today you guys provide very good support. Maybe other hosting providers do not face such issues, and I do not know if this is right, but if you K2 guys have any hosting providers "approved" let's say and compatible with K2 it would be good to know. Agan many thanks for your support