Updated the FW to latest 1.7 ........ it worked, volume error was fixed - I can now toggle the volume settings freely, though the volume level seems to have dropped a bit from the last time I used the unit. I'll try to use SPDIF just to check.
Weird that this happened in the first place ........ have used quite a number of different MED models and this is the first time I've seen the error.
Thanks for the help guys.