wmpband.dll prevents downgrading WMP11?

I'm having trouble downgrading my WMP 11 FINAL to the beta 2 version. I downloaded the WM Fix (which explained that I needed to overwrite my Windows Media Player folder with the new one provided. When I try to do this, I get an error saying that wmpband.dll is being used by another person or program. I tried copying the files when no other programs were running on my computer so I have no clue what is preventing this. Any help would be greatly appreciated.

I have looked everywhere and can't find a working link to download WM beta 2 and going from there. Does anyone have any links that work?