Mine hasn't failed to open yet, although its behavior can still be quirky at times. It usually takes a minute or so for Walk Designer to open that first time during a session; I'm not sure why. Maybe because it's loading the Don figure (for the display) and all the walk cycles in the Walk Designer folder. After it opens, however, everything is in memory, and you can close and reopen it almost instantly. Do you have the latest Service Release installed? Some Walk Designer problems were addressed in the patches. Did you delete the "Don for Walk Designer" figure from your Character folders? That's the file that Walk Designer loads by default.