That error means that the .reg file is trying to modify a registry key that your account does not have ownership of and/or permission to modify.
The .reg file will still import and modify everything except for the ones that you do not have permission to allow.
You could right click on the .reg file and click on Edit
to see it's content. From there, you could manually check each key in the .reg file to see if you have ownership and/or "Full Access" permission of that key inside your registry (regedit). See step 3 in OPTION THREE below for more details to help with this.
Take Ownership of file - Vista Forums
I would highly recommend to not do this if you are not sure of what you are doing. One mistake made in the registry could leave you needing to reinstall Windows. Either way, I would strongly recommend to create a restore point
before touching the registry in case a mistake was made, and you need to do a system restore
to undo it.
Hope this helps,