Throx

This annoying issue occurs when you try to click the “Save Changes” button in your widgets configuration page, it gone to a blank page or give you an error message “page not found….” . This often caused by the mod_security rule settings in apache httpd.conf. If you do not have access to the httpd configuration file and want to solve this problem, the following tips may help you out.

Create a text file and named it “.htaccess”. Edit it and put the following code inside it:

<IfModule mod_security.c>
SecFilterInheritance Off
</IfModule>

Save it and then upload it to your wp-admin directory. If your directory have .htaccess in it, just edit it and add in the code and save it. I found this solutions from WordPress’s forum, hope this solution works for you guys.

Source: http://wordpress.org/support/topic/117993?replies=47