In Windows 7 you are not allowed to write anything in the Program Files folder, or any folder under C:

You can:

1.- Give Poser's runtime folder the proper permissions.
2.- Create an external runtime outside C: and import it into poser (What I use)
3.- Disable windows UAC (personally, I don't recomend this)

Depending on what do you think it's best for you we can elaborate from there.