Bob Markey wrote on Mar 2^nd, 2009 at 6:40pm:

The biggest keys here are to make sure the freq and course are in the ILS radio, and to have patience- LAND3 won't engage until you've intercepted glideslope and I believe I won't engage unless the gears and flaps are down. Hope it helps. ;)

I second that, and i would also add, that from what i have experienced there is one more condition to make the autoland active. You have to be fully stabilized on the GS and LOC. In certain weather conditions it might be difficult and can happen really late or even never. With mild weather 100% of my landings were in autoland mode. So unless you are flying in hurricane, you might be doing something wrong.