Sorry we haven't responded to your prior support request attempts. We'll try and get this sorted for you soon.
I can think of two reasons that may cause this error to appear but I'll need to take a closer look.
Can you please send me a support ticket via http://ee-garage.com/nsm-better-meta/support as I'll probably need to get more information about the ...
$meta_title = implode(" | ", array_filter(array($this-...
You'll definitely need to upgrade to NSM Better Meta 1.1.5a - the release notes mention EE 2.6 compatibility, which likely includes accounting for the database changes which it brought (specifically, the removal of the dst_enabled column).
Try using the attr_safe modifier on your tag (where the value is generated, not the layout tag) - https://docs.expressionengine.com/latest/templates/variable-modifiers.html#attr_safe - that will convert special characters to HTML entities which should work.