Remove/hide unused sidebar widget area from admin

are you trying to restrict what is being seen in the dashboard or on the live site

if live site, then can you post the link so that we can see the issue

you could try

Advanced Access Manager

http://wordpress.org/plugins/advanced-access-manager/

I used this to restrict access for one of my sites.

It’s quite a powerful and hefty tool, but it will do the job.