Hi,
It does not matter which category I select, it happens (blank screen is showing) with every category, from within different browsers (IE9, IE10, FF, Chrome). It has used to worked fine. The plugin is also working fine, only this blank screen is the problem.

I'm using k2 v2.6.8 and joomla! v.3.2.3

Hi. Are you talking about front-end or back-end? A blank screen usually indicates a PHP error. Set error reporting to "Maximum" to see the error message.

I see blank screen only on back-end.
I did as you wrote, i set error reporting to "Maximum" and ... i get this messages

"Strict Standards: Only variables should be assigned by reference in /raportrolnycom/modules/mod_highlighter_gk4/gk_classes/gk.source.k2.php on line 17"

Strict Standards: Only variables should be assigned by reference in /raportrolnycom/modules/mod_highlighter_gk4/gk_classes/gk.source.k2.php on line 18

Strict Standards: Only variables should be assigned by reference in /raportrolnycom/modules/mod_highlighter_gk4/helper.php on line 109

Strict Standards: Non-static method NH_GK4_Utils::cutText() should not be called statically, assuming $this from incompatible context in /raportrolnycom/modules/mod_highlighter_gk4/helper.php on line 136

Strict Standards: Non-static method NH_GK4_Utils::cutText() should not be called statically, assuming $this from incompatible context in /raportrolnycom/modules/mod_highlighter_gk4/helper.php on line 137

Strict Standards: Non-static method NH_GK4_Utils::cutText() should not be called statically, assuming $this from incompatible context in /raportrolnycom/modules/mod_highlighter_gk4/helper.php on line 136

Strict Standards: Non-static method NH_GK4_Utils::cutText() should not be called statically, assuming $this from incompatible context in /raportrolnycom/modules/mod_highlighter_gk4/helper.php on line 137

None of these errors produces a blank screen. They also come from an other extension, not K2. Maybe you are talking about something else? Is there a screenshot with the issue?

once again i set error reporting to maximum .... please look at my site raportrolny.com and help me with this problem.

This does not help. First of all as i told you all these "Strict Standards" errors come from other extensions, not K2. Secondly as i already told you i will need a screenshot to see what's happening since the issue occurs in item form.

Look at my attachment (screenshot) please. I also record a short video ... i hope it will help you solve my problem - www.youtube.com/watch?v=KrX5JdwTttM&feature=youtu.be

Check the browser console for errors. This looks like a javascript error. Also, I was not able to read the URL, the resolution of the video is low.

i think that the browser is not a problem .... i check this on different browsers like opera, IE and firefox i also do the same on 3 different computers. Url adress is the same

url before choosing category raportrolny.com/administrator/index.php?option=com_k2&view=item

url after i chose category (blank screen) raportrolny.com/administrator/index.php?option=com_k2&view=item

I am not saying that the browser has problem. I am saying to check the browser console for errors.