In some rare cases, there seems to be an issue when upgrading from NGFB v1.x/2.x to NGFB v3.x -- WordPress seems to think a protected option name ('alloptions' or 'notoptions') is being updated, though it is not. NGFB only ever updates one option name, which is 'ngfb_options'. This problem has been reported by many, for several different plugins, themes, etc., not just NGFB. :) Hopefully the WordPress developers will address the issue before too long. In the meantime, you can try the following procedure:
1) Delete the existing nextgen-facebook plugin folder.
2) Go to the WordPress plugin admin page. WP will deactivate NGFB since the plugin is missing.
3) Add the following to your wp-config.php file and re-install NGFB.
4) Go to the NGFB settings page and save the new default settings.
5) Remove the NGFB_RESET entry from your wp-config.php file.
If you need to re-install an older version, you can find them here: http://wordpress.org/extend/plugins/nextgen-facebook/developers/