Make sure your alternator is seated properly. Any gaps will set the pulley offline.
I don't know if its just me but installing the ac belt is harder than replacing the alt, waterpump, ect. Even with the special tool. Good thing I don't have to do it again, drive it till it snap then I will change it.
2011 X5 35i Sport Plat-Gray
2008 550i M Carbon Black-SOLD
2013 Triumph Daytona 675R