I managed to get this working by editing the file located (within plugin) at:
modules/meta/meta-descriptions.php
find line: 111 which reads:
array( $auto_excerpt, strip_tags($post->post_excerpt))
within the code:
$desc = str_replace(
array('{excerpt::autogen}', '{excerpt}'),
array(strip_tags($post->post_excerpt), $auto_excerpt),
$format);
and swap the order of the second arguments so line 111 reads:
array(strip_tags($post->post_excerpt), $auto_excerpt)
that should work