The same problem, the same error with K2 2.6.9 and Joomla 3.4.1 (fresh install, no third-party extensions).

Set error reporting to "Development" in Joomla's Global Configuration, go to site.com/administrator/index.php?option=com_k2, we get

The same problem happens with K2 2.6.6, 2.6.7, 2.6.8.

However, if you use an older version of Joomla, everything is good.

To work around, I installed Joomla 3.2, installed K2 2.6.9, everything was successful, then update to Joomla 3.4.1. Now K2 works. This solution can only be used if you start a new site/project which uses K2. If you already have a site with lots of installed extensions and data, this solution is not possible.

I hope this info is helpful.

This only happens if you have the system plugin disabled.
Enable the plugin and K2 will work properly.

Problem with plugin Smart Search - K2 too.
Not activated on starting install
Activate: K2 will work correctly then
Joo 3.4.8 + K2 2.6.9

have a good day :-)

Thank you for reporting this Fred :)

Hello,
For me, very simple solution: changed CHmod on components/com_k2/helpers/permissions.php (was 604 -> causes fatal error)
kisses
(Joo 3.5.1 // K2 2.7.0)

Make sure that your folder/file permission is set to 755/644 so you won't have any more issues :)