Snapshot fails to complete

When I run snapshot using 'run now' it goes to completion.
It fails when run detached (manually or scheduled)

Debug.log is as follows
[09-Apr-2014 19:45:52 UTC] PHP Warning: json_encode() [function.json-encode]: Invalid UTF-8 sequence in argument in /home/sealisl2/public_html/wp-includes/update.php on line 255
[09-Apr-2014 19:46:39 UTC] PHP Notice: Undefined index: snapshot-blog-id in /home/sealisl2/public_html/wp-content/plugins/snapshot/snapshot.php on line 1607