Too humid?
Maybe I am stating the obvious, but it's a good place to start.
Where is the water dish (warm/cool end)?
If at warm, move to cool
Can you increase ventilation?
There's another active thread about substrate. Maybe a change another type like aspen, as it doesn't hold moisture for so long as bark or other subs.
Cant think of anything else, but when i do, i will post more.