If you'r pc is infected with virus or for some other reason you can not edit your registry you may see this kind of error. now if you clean your virus that won't fix your registry issue. You get stuck.
there is some free and paid tools that can fix it. but some time it is hard to find because there is too many tools that offer that support but which one is good or work is hard to find.
If there is a easy way that can fix that problem without any soft is better no need to carry any soft.
1. First go to run on win xp/7/8 type"gpedit.msc" and hit enter.
2. then double click on User Configuration
3. then double click on Administrative Templates
4. then double click on System
5. then Find and double click on "Prevent Access to registry editing tools".
6. In the popup window, Click Disabled and click on OK.
Now you are good to go. Now if you may feel it is too hard so i make it short. Type gpedit.msc on your run bar. then open User Configuration then Administrative Templates then System and open Prevent Access to registry editing tools and click disable. Done