Error on posting

Hi, whenever we post or update a post anything, we get a white screen with the following error:

Notice: Undefined index: custom_feeds in ~path/wp-content/plugins/powerpress/powerpressadmin.php on line 2484

Warning: Cannot modify header information – headers already sent by (output started at ~path/wp-content/plugins/powerpress/powerpressadmin.php:2484) in ~path/wp-includes/pluggable.php on line 876

How can I fix this error?

Some details

• happens regardless of post type
• happens whether we actually use the plugin meta box or not
• happens regardless of theme
• only started happening when we integrated our blubrry hosting account

http://ww.wp.xz.cn/extend/plugins/powerpress/