I am also experiencing an issue when editing (saving) a post. I get the same first two errors and two different ones. This issue began when the site I manage was updated to WordPress 3.9.1 (about a month ago).
Notice: Undefined variable: explicit in /home/content/w/i/e/wiensgd/html/wp-content/plugins/seriously-simple-podcasting/classes/class-seriously-simple-podcasting.php on line 332
Notice: Undefined variable: block in /home/content/w/i/e/wiensgd/html/wp-content/plugins/seriously-simple-podcasting/classes/class-seriously-simple-podcasting.php on line 332
Warning: Cannot modify header information - headers already sent by (output started at /home/content/w/i/e/wiensgd/html/wp-content/plugins/seriously-simple-podcasting/classes/class-seriously-simple-podcasting.php:332) in /home/content/w/i/e/wiensgd/html/wp-admin/post.php on line 235
Warning: Cannot modify header information - headers already sent by (output started at /home/content/w/i/e/wiensgd/html/wp-content/plugins/seriously-simple-podcasting/classes/class-seriously-simple-podcasting.php:332) in /home/content/w/i/e/wiensgd/html/wp-includes/pluggable.php on line 1121