1. You already have that version installed.
2. The version you downloaded is not for your model of phone.
3. You didn't delete the vendor file.
4. You didn't click on app loader.
** Update**
I deleted the vendor file last night, at least I thought I did, but I just went back to the app loader thing and it was still there. As soon as I deleted it and hit the app loader...i looks like it's working now.
Trust me, I'll update the thread if something else goes wrong...