I'm sorry I am not that savvy in Joomla as far as the backend. Where do I find (mod_k2_content/tmpl/default.php)? I am looking under folder permissions and the only thing not writable is the configuration.php.

The entire UI (thus the markup) has been changed.
This means you need to clear both Joomla!'s and your browser's cache.
You were correct to do this. If you are using an obsolete override of itemform.php you might need to update it, although this is unlikely.

Can you check if jQuery is being loaded and if not, can you enable jQuery loading from K2's settings.

Report after updating to dev-build 2.7.1:
In the backend the tabs don't work anymore. All tabs (the links) and the content is above each other, console gives no JS-errors, all caches cleared, 3 different browsers tested.
And when editing in the frontend: the editor now shows up, but I can't save or close anything. The buttons for "featured" and "enabled" also don't work. Console gives following error in k2.js:
Got an advice before I need to roll back and Frankensteinin' it?

This the file that will produce any error.

github.com/getk2/k2/blob/master/components/com_k2/views/item/view.html.php

You can Frankenstein it (backup first) but I do not know if other issues will arise.

Great, Now in the other topic, the question was about a specific file.
K2 would still be there, however the file in question (mod_k2_content/tmpl/default.php) is it there?

Furthermore, just to rule out a permissions issue, are your files permissions set to 644 and your folders to 755?

Warning: require(/home/cohemplo/public_html/modules/mod_k2_content/tmpl/default.php): failed to open stream: No such file or directory in /home/cohemplo/public_html/modules/mod_k2_content/mod_k2_content.php on line 55

Fatal error: require(): Failed opening required '/home/cohemplo/public_html/modules/mod_k2_content/tmpl/default.php' (include_path='.:/usr/local/php54/pear') in /home/cohemplo/public_html/modules/mod_k2_content/mod_k2_content.php on line 55

I never uninstalled K2. I did however reinstall over what I had, but we already had the latest K2.

Never uninstall K2 in order to update it, you will lose all your content.
Install the new version on top. To be extra sure that nothing goes wrong you can also backup prior to updating ( highly unlikely that anything goes wrong ).

I can not respond to this topic. Krikor sent me response.

I have not uninstalled k2 and reinstalled? No it is not the root folder. We use k2 for articles throughout the websites, so if k2 is being used on any of those websites then the error occurs.

They are correct to do so.
It seems that some required files are missing.
Is the /home/cohemplo/public_html/modules/mod_k2_content/tmpl/default.php with '/home/cohemplo/public_html' being your Joomla!'s root path there?

Did you uninstall K2 at any point?

I am not sure if this went through?

Hello,

I am getting a fatal error as well when I have updated to Joomla 3.6 and also updated the Advanced Module. I have the Advanced Module off, but when I have it on I get this error:

Warning: require(/home/cohemplo/public_html/modules/mod_k2_content/tmpl/default.php): failed to open stream: No such file or directory in /home/cohemplo/public_html/modules/mod_k2_content/mod_k2_content.php on line 55

Fatal error: require(): Failed opening required '/home/cohemplo/public_html/modules/mod_k2_content/tmpl/default.php' (include_path='.:/usr/local/php54/pear') in /home/cohemplo/public_html/modules/mod_k2_content/mod_k2_content.php on line 55

I have contacted Regular Labs and they are advising me to seek your assistance.

Hello,

I am getting a fatal error as well when I have updated to Joomla 3.6 and also updated the Advanced Module. I have the Advanced Module off, but when I have it on I get this error:

Warning: require(/home/cohemplo/public_html/modules/mod_k2_content/tmpl/default.php): failed to open stream: No such file or directory in /home/cohemplo/public_html/modules/mod_k2_content/mod_k2_content.php on line 55

Fatal error: require(): Failed opening required '/home/cohemplo/public_html/modules/mod_k2_content/tmpl/default.php' (include_path='.:/usr/local/php54/pear') in /home/cohemplo/public_html/modules/mod_k2_content/mod_k2_content.php on line 55

I have contacted Regular Labs and they are advising me to seek your assistance.

Hello,

You need to update K2 to its latest version or even better install the latest DEV version github.com/getk2/k2.

Unfortunately the only way is to update K2Store and K2 to their latest version. Even better user 2.7.1 github.com/getk2/k2

K2Store works fine with the latest version of K2, but just in case backup before you update.

Dear Sir / Madam

I have problem in front-end page after upgrade joomla to 3.6 before then i used k2 2.69 and joomla 3.5.1 normally but now i have Big problem because my author doesn't sent article from font-end .

I can't update k2 to 2.7 because i using k2store maybe it's not working with k2 2.7 .

I hope your team help me and another people .

Best Regards,
Amir

After updating our website to joomla 3.6, we are getting a fatal error when adding new K2 items from the frontend: Fatal error: Call to a member function isCheckedOut() on null in /administrator/components/com_k2/views/item/view.html.php on line 100 and a blank screen.

We currently have K2 version 2.6.9. How to correct this issue?

K2 is enabled at Default css. I looking like the Framework is blocking the inheritance. Will have to work with the designer to see if there is a solution. Thanks for the help.

It looks like K2's css are not being loaded.
It could be related to two things.
a) Template's or framework's caching is not reflecting the changes,
b) You have disabled K2's css loading from the extension's settings.

I have cleared the firewalls of the block. Also had to change the link in the original post as they changed after the restore. But you will be able to see the difference in the live site running J3.5.1 & K2.6.9 and the Dev site running J3.6 & K2.7.1.

I have both my server and site firewall locked down with black listing with IP and country blocking due to repeated hacking and bought down my server a couple months ago.

However I had to end up restoring the site back to J3.5.1 and K2.6.9 as I had to get users back in and working.

I am providing both live and dev screen shots of what happens when the site is working with J3.5.1 and K2.6.9 on the live site and with J3.6 and K2.7.1 running on the dev site.

If you let me know where you are I can free up the firewalls

LIVE ScreenShot - Dev ScreenShot