Why are leaves yellowing on my Dendrobium Biggibum?

[kiki-do]

I have a hard time with dendrobiums myself. Someone here mentioned a while ago, that they will shed their leaves if they are kept too dry during their growing season. I upped the watering a tad and they responded well. I'm not sure if that is "your" problem, but it sounds like what I was going through.
I would check the roots, too, just to be safe. Hope that helped!