The URL to submit to Propeller is incorrect in version 2.9.1 of Sociable. You need to edit sociable.php as indicated below to submit to Propeller properly:
// this is the current code that needs to be changed
// it is located somewhere around line 370 of sociable.php
'Propeller' => array(
'favicon' => 'propeller.gif',
'url' => 'http://www.propeller.com/submit/?U=PERMALINK&T=TITLE'
),
// replace the code block above with this one
'Propeller' => array(
'favicon' => 'propeller.gif',
'url' => 'http://www.propeller.com/submit/?url=PERMALINK'
),