Very strange error in frontend

I get this error on my site http://www.eva-neuner.de

Deprecated: Non-static method JApplicationSite::getMenu() should not be called statically, assuming $this from incompatible context in /mnt/webo/a2/17/54221917/htdocs/templates/gk_storefront/lib/framework/helper.layout.php on line 152 Deprecated: Non-static method JApplicationCms::getMenu() should not be called statically, assuming $this from incompatible context in /mnt/webo/a2/17/54221917/htdocs/libraries/cms/application/site.php on line 272

Any suggestions how I can get rid of this?
Help is urgently needed as customer is getting MAD actually.

Thank you very much for your support in advance!

Hi

Please update template to the latest version. I believe recently Your server's PHP was changed to PHP 7 and it's trying to force new programming style.