Hello Sylvian,
This is a notice and not an actuall error, I won't affect your site's functionality.
It is related to your template overrides however so the template developer will know exacty how to correct this issue.
As for the host, it is hard to know if it is their fault without any hardware and hosting specs. Keep in mind that apart of K2 you might have other extensions installed that might cause that issue.
JoomlaWorks Support Team
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Please search the forum before posting a new topic :)