What reasons would there be why you can't write to the registry?

I'm trying to set several trusted sites and I need to create a key and value but I keep getting an error for "Can't Write"

Example:

The key I'm trying to add would be:

Software\Microsoft\Windows\CurrentVersion\Internet Settings\ZoneMap\Domains\google.com\

Value:
"*"

Value data:
2 (a REG_DWORD)