errors after saving a widget

Hi I activate your plugin,
try to use it and after saving a widget I get this errors:

“Notice: Undefined offset: 0 in ….wp-includes/capabilities.php on line 1075

Warning: Cannot modify header information – headers already sent by (output started at …/wp-includes/capabilities.php:1075) in …./wp-admin/post.php on line 222

Warning: Cannot modify header information – headers already sent by (output started at …/wp-includes/capabilities.php:1075) in …/wp-includes/pluggable.php on line 899

http://wordpress.org/plugins/per-page-widgets/