I have been adding a K2 menu item and getting just a white screen as result when klicking that. Changing back to std Joomla single article or category menu item - it is ok again. I am now using beez_20 template but also got the same effect from other templates.
Must also say that tutorials from K2 group is not much of help in this. Search in this forum gave nothing.
I am using Swedish language files and updated to latest version today V2.5.1 and a lot is not translated yet. Could that be the problem?

Which K2 Menu did you use ? Item, Category etc ?
a little more Infos of what you did would be helpfull

Joomla v7.2, K2.5.1 menu type K2 category and K2 item. Very simple setup. As I have had some problems with this I just made a test. - Installed 7.2 + K25.1 + latest Swedish translation,+ JCE editor, + Akeeba backup + Used the basic template Beez_20
Then I toggled between a menu "Start" as std Joomla and K2 item/K2 category with connected Article/item.
.htaccess active and tested to work.

If there is now quick answer maybe I have to make a setup on remote server so you can login and have a back door look.

a link to the Page would help.

If you want you can send me temp. Login for Backend - troponin(at)brain-style.de

Many thanks Thorsten for trying to help.
I have now uploded a test site aimed for you to check. And of course it is then working as expected :huh: . The problem is the be found on my pc:s. Joomla and all extensions are running without any problem except for the K2 menu items. I have the same setup with apache and php on both localhosts. What is needed more in K2? That is the question just now.
My setup for localhost is provided from NuSphere TechPlatform installer all in one package.