jwjnyc on "Fatal error - 'Illegal widget setting ID"

I am getting the following error and have no way to fix: Help please!

Fatal error: Uncaught exception 'Exception' with message 'Illegal widget setting ID: nav_menu_item[]' in /home/smartass81/public_html/wp-includes/customize/class-wp-customize-nav-menu-item-setting.php:180 Stack trace: #0 /home/smartass81/public_html/wp-includes/class-wp-customize-nav-menus.php(589): WP_Customize_Nav_Menu_Item_Setting->__construct(Object(WP_Customize_Manager), 'nav_menu_item[]', Array) #1 [inteal function]: WP_Customize_Nav_Menus->customize_register(Object(WP_Customize_Manager)) #2 /home/smartass81/public_html/wp-includes/plugin.php(525): call_user_func_array(Array, Array) #3 /home/smartass81/public_html/wp-includes/class-wp-customize-manager.php(605): do_action('customize_regis...', Object(WP_Customize_Manager)) #4 [inteal function]: WP_Customize_Manager->wp_loaded('') #5 /home/smartass81/public_html/wp-includes/plugin.php(525): call_user_func_array(Array, Array) #6 /home/smartass81/public_html/wp-settings.php(414): do_action('wp_loaded') #7 /home/smartass81/public_html/wp-config.php(89): require_once in /home/smartass81/public_html/wp-includes/customize/class-wp-customize-nav-menu-item-setting.php on line 180

- What did you do before this issue happened?
- Have you checked your server error logs?

http://codex.wordpress.org/Forum_Welcome#Include_as_Much_Information_as_Possible

I was in the middle of converting a very old site to a new theme (the West). I loaded the theme and I was able to customize a few pages, but when I added an old web page to the menu and tried to save, I immediately got the error. Now I can't customize anything. I even tried loaded another theme, but get the same error. I have deactivated all plugins as well.

I don't know how to check my server logs as I am really not a coder. I have made many sites before using themes, but never have come across this problem before - I think it was because I am converting an old site.

Any more help you can give?