Fatal error: Uncaught Error: Using $this when not in object context in /volume1/web/packages/system/site/document.tpl.php on line 18

Error: Using $this when not in object context in /volume1/web/packages/system/site/document.tpl.php on line 18

Call Stack:
    0.0001     359520   1. {main}() /volume1/web/packages/system/site/document.tpl.php:0