Quick Update - I had installed 2 K2 plugins initially and once I disabled them, I can now create categories and the 500 error no longer occurs.

The plugins you ask?

CSS4K2 - 1) onecssperk2template_v127.zip & 2) plugin_k2_css4k2_1.8.1.zip

*Update* -

Upon creating my first category - I did receive this error message on the Categories page -

I also encount 500 problem after fresh install of 2.6.7, when I turn off cache at Global Configuration, the problem is clear, maybe it will be useful for you.

A-Bo Lee wrote: I also encount 500 problem after fresh install of 2.6.7, when I turn off cache at Global Configuration, the problem is clear, maybe it will be useful for you.

i also have turned of cache but it dont help... problem with 500 error is still exist :(
can anyone help me ?

EDIT:

my error is :
500 - Nieznany błąd

Nie można załadować pliku XML

---

500 - unknow error
cant load xml file

---

can anyone know what XML file K2 cant load ? and why on ver 2.6.0 K2 can load this file... ?

i am running joomla 2.5.14 and upgraded k2 yesterday as it showed i needed to update it. now i get the 500 error. i've upgraded on two sites and same issue on both. i had cache turned off before and still have the 500 error. is this version bad? why hasn't an admin posted a response?

it is a problem - i don't know why them do not interested in this problem :(

Maybe someone from administratrion will answer ???

@cegi

The error you are getting can be caused by a lot of things. In order to resolve it try:

1. Update your Joomla! installation.
2. Ensure that your server setup allows you to upload files. For example try to install an other extension and see if you get any error.
3. Check your folders permissions. Use a tool like admin tools to fix all the folder permissions.
4. Try to download again the zip file of K2, just in case the one you have is corrupted.

We have tested it multiple 2.5.14 sites. It running smoothly. Make sure your other K2 plugins (like CSS4K2 or Disquss comments for K2 as an example) are compatible with v 2.6.7.

If you are having 500 issues after clearnig your cache and using Joomla!'s latest version try disabling any K2 plugins one by one.

i`ve change a joomla template and update joomla to 2.5.14 and i can update K2 to 2.6.6 but on version 2.6.7 it still has this strange 500 error...

Make sure ALL K2 plugins are at their latest versions. This means apart from K2 additional plugins which are not developed or maintained by us.

There can be user plugins (a component which offers K2 integration) related content plugins, css & templating plugins and even templating frameworks. We are running 2.6.7 (and updated from 2.6.6 to .7) on multiple production sites with no hassle.

Apart from what Lefteris said see if you are using the plugins Rob Rosko mentioned.