After upgrading from k2 2.5.1 to 2.6.7, everything seems to work fine, except the extra fields. In the backend, I get this errors:

Is there any solution? Should I downgrade to previous versions?

Hello,

This is a notice not an actual error. This will not affect your site's functionality in any way.

For production sites I recommend that you set error reporting to simple or none.

Thanks, Krikor. I had upgraded to k2 2.6.6 and there was no "notice." But now that you said this notice is not important, I will consider upgrading to the latest version, 2.6.7. But, Would you please tell me how should I change the error reporting to "simple"?

Also, I'm facing another issue regarding upgrades. This is about Joomla itself, not k2. When upgrading from Joomla 2.5.8 to 2.5.14, I get the below error. How important is that? Should I forget about upgrating Joomla?

Thanks in advance.

Hello imax,

The settings are located in the global configuation, in the server tab.

You have to update to 2.5.14 since this is a security update ASAP. I would recommend backing up and trying to repair and optimise your DB tables before you upgrade. You can use PhpMyAdmin or a component called Admin Tools