MyBook Studio II showing raid error/ missing disk but working fine?

I’m still looking for a solution to this. I was copying a file today when the DriveManager SW put up a window saying the drive was faulty. Opening drive manager says that DriveA is missing, but the file copies without any issues. This sounds like a FW or DriveManager issue but I am running the latest of both.

I have 2 WD Green 2TB drives inn connection is FW800.  

Anymsuggestions?