WebCloseApplication is the underlying id/name of the Terminate action in a Navigate stage. It looks like objects just aren't compatible to be imported from 6.9 into 6.8 if they're using certain action types in Navigate stages. For example, I reproduced the same error with these three actions: Terminate (id=WebCloseApplication), Get HTML (id=WebGetHtml), and Hover (id=WebHover).
I'll probably submit this as a bug in case BP isn't aware of it.
For now, I would say your only way for a workaround at the moment would be to do some trial and error. Remove navigate stages as you identify that they won't work for importing into 6.8. And then once in 6.8, switch to the equivalent action.
------------------------------
Dave Morris
Cano Ai
Atlanta, GA
------------------------------
Dave Morris, 3Ci at Southern Company