404 error in subcategory links

i have new Review Com Blog
i have review categies and subcategories
i use the tag
/%category%/%postname%/
posts appears good in main category Like Technology
but when openeing subcategory linke Digital camera

it gives 404 error

i think it is popular proplem with many wordpress users

what can i do??

Note: i used /%category%/%category%/%postname%/ tag
my posts apears good in main and subcategories
but gives me duplicate url
like
http://www.setreview.com/technology/digital-camera/technology/digital-camera/post/

what can i do??
please help