Why can't I change Window 7 registry key?

I want to change a Windows 7 Registry key in HKEY_LOCAL_MACHINE->SOFTWARE->Classes->CLSID->B54F3741-5B07-11cf-A4B0-00AA004A55E8} -> InprocServer32. I ran regedit as administrator. But when I was trying to modify that key, it doesn't allow me to change and reports error as

Cannot edit: error writing the value's new contents

So why can't I change the registry key even in administrator mode? How to solve this problem in Windows 7? I also disabled my Anti-Virus but it didn't help.

Answer

Because by default Administrators only have read permissions for that key

You can open the permissions window by right clicking on InprocServer32 and choosing Permissions....

Now to head off a XY Problem, why are you wanting to changes the value in the first place?