Start regedit.exe again.
Allow the program to run.
"Registry-editor" will open. On the left side browse to the key
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class
Right-click on Class and select Permissions...
On the Permissions dialog click the Advanced button.
Click the Owner tab on the Advanced Security Settings dialog.
Click the Other users or groups... button
Type Everyone in the text box and click OK.
Check the box "Replace owner on subcontainers and objects".
Click the Permissions tab again and uncheck "Include inheritable permissions from this object's parent".
If prompted with a Windows Security warning with Add and Remove buttons, click Add.
Click OK to close the Advanced Security Settings dialog.
Make sure the Everyone group is selected in the Permissions dialog and ensure that the checkbox for Full Control under the Allow column is checked. Click OK.
Now, right click on the registrykey Class again and select New - Key.
Are you able to add a new key ?