Hello, can someone help me or fix it?
Regards

Special clean copy of joomla + widgetkit + K2 as an example: http://s68unix(dot)unixstorm(dot)org
Clean installation: Joomla v3.6.4 + K2 v2.7.2 + widgetkit_2.9.1_j3.
K2 v2.7.2 - (github.com, archive, master.zip)

Yootheme support (My topic: "ImageProvider.php on line 36"):

If so, please mind that K2 is not a YOOtheme product and the file does not belong to a YOOtheme product.
For further issues with K2, please contact the developers of K2 and ask them for support.

Hello,

A file from widgetkit it trying to access a K2 file.
ImageProvider.php is not a part of K2 and the file that is causing the issue is coming from widgekit.
Furthermore the PHP warning is caused by a security setting in your server's configuration.
You can ask your hosting provider if it is possible to remove this restriction.