fatal error.

Hi,

WPi Designer Button triggers a fatal error.

Fatal error: Uncaught TypeError: call_user_func_array(): Argument #1 ($callback) must be a valid callback, non-static method WPi_DesignerButtonActivation::myplugin_activate() cannot be called statically in xx/public_html/wp-includes/class-wp-hook.php:303 Stack trace: #0 xx/public_html/wp-includes/class-wp-hook.php(327): WP_Hook->apply_filters() #1 xx/public_html/wp-includes/plugin.php(470): WP_Hook->do_action() #2 xx/public_html/wp-admin/plugins.php(193): do_action() #3 {main} thrown in xx/public_html/wp-includes/class-wp-hook.php on line 303

Disabling all plugins still triggers the error. Any idea?