You are likely doing nothing wrong, but give more info: how much sun is the plant getting (hours per day)--the same amount as your other roses? Is it in the same area with the same soil conditions as the others? Is there a large tree nearby?

If it looks okay, if it is getting enough sun and roughly the same conditions as the others, just be patient. It could be growing a massive amount of roots. Some very good roses are slow to get going, but worth the wait.

I've had Falling in Love for about 4 years and it is a slow grower for me as well. I had to cut it right down this spring and while everything else has grown and bloomed this one is still just sitting there. I pinched the tips and now I finally see a bit of new growth on it. No way of knowing yet if it will set bloom or not. Although the blooms are lovely I'm not terribly impressed with this rose and with it's black spotting and lethal thorns I'm not sure it's worth keeping.