This is a question of privileges. If you're an admin on your local box, I can help.
Try this: Right-click your Powershell icon and select Run As Administrator. Then try running your script; it will work.
However, this doesn't answer how you can do this from within a script. You can add some code to your script that will automatically try to make your PS session elevated, but you will still have to interact with the security dialog box that shows up anytime you try and run something as an admin that's Vista or later. So, not sure how much easier this is than just starting your session as an admin, but add this to the beginning of your script:
$Host.UI.RawUI.WindowTitle = $myInvocation.MyCommand.Definition + "(Elevated)"
$newProcess = new-object System.Diagnostics.ProcessStartInfo "PowerShell";
$newProcess.Arguments = $myInvocation.MyCommand.Definition;
$newProcess.Verb = "runas";