Logon Screen Changer

I downloaded the Tweaks.com app to change the logon screen. It worked on my desktop, but on my laptop (both have W7 Ultimate 64bit) no matter what file/pic I choose (I have ownership permissions) I get an error message - "Access to the path C:\Windows\system32\oobe\info\backgrounds\backup\Win7-Blue-1920x1200_3_27_2010_11_44_58.jpg' is denied.

Anybody know what I should do.

I am only an intermediate computer hobbyist, so any advice has a better chance of being followed if step by step details are given.

Thank you

I am not familiar with that program, but perhaps the folders were created by it, and the permissions were locked there?

I only have (Windows 7 - 64Bit) the oobe folder - no sub folders under that, apart for a personal second language one?