[Plugin: Blogger.com publisher] errors

I am not sure why I am getting these errors:

Warning: DateTime::modify() [datetime.modify]: Failed to parse time string () at position 0 ( in /home/polar/public_html/wp-content/plugins/bloggercom-publisher/gdatablogger.php on line 89

Warning: Cannot modify header information - headers already sent by (output started at /home/polar/public_html/wp-content/plugins/bloggercom-publisher/gdatablogger.php:89) in /home/polar/public_html/wp-includes/pluggable.php on line 866

please help

https://www.ads-software.com/extend/plugins/bloggercom-publisher/