Error opening League

League encounters an error when attempting to start the game. Nothing opens and an error box pops up with the following text.

C:\Riot Games\League of Legends\zlib.dll is either not designed to run on Windows or it contains an error. Try installing the program again using the original installation media or contact your system administrator or the software vendor for support. Error status 0xc0000020

I've reinstalled League and tried running administrator to no effect. Any help would be awesome, thanks in advance!