Perhaps you are running into the annoying UAC 'User Account Control' on VISTA.

Your command prompt may need elevated privileges.

Also, please check this MS KB article on "Windows Resource Protection (WRP) file is missing or is corrupted"

You can either permanently disable the User Account Control or elevate privileges for just one instance of the command prompt, by right-clicking the command prompt icon, and requesting admin level run (Sorry - I'm on a Linux PC, and cant see the exact syntax at this time).