Now this is creepy, I configured the HDD's again in the RAID utility (hardware). Windows asked my to format one drive. Canceled as I wanted to try something else. But didn't work.
Anyway just noticed the drives have come back together and show the existing files. Tried deleting the folder I was having trouble with, and had no problems.... weird!
Thanks for your help guys, even if it wasn't the way we intended it to work.