Exactly the same here. WP 3.9.2 and plugin 4.7
'Undefined index: ssba_excerpts' at /html/wp-content/plugins/simple-share-buttons-adder/simple-share-buttons-adder.php 774: /html/wp-settings.php 214 calling include_once() | /html/wp-config.php 216 calling require_once() | /html/wp-load.php 29 calling require_once() | /html/wp-blog-header.php 12 calling require_once() | /html/index.php 17 calling require()
Let me know if there’s anything I can do to help debug.