Been there, done that. You're not alone in the Paph killing department, so don't feel too bad about yourself.
I'm fairly new to Paphs myself, and I'm a windowsill grower. I have a little helenae that I've had for over a year now. So far, I haven't killed it, but I think I got a little too close for comfort with my terrarium bark experiment on this little one (it stayed too wet for too long).
Helenae seems to like a coarser mix to make it dry up faster between waterings, it's calcerous so now I've added some marble chips to the substrate on mine (otherwise, crushed oyster shells will do) - so far so good. Most probably, you kept it too wet (a disease I suffer from too, when it comes to some of my Paphs...). Try and give the next one a coarser mix and see how it goes.