Are you getting the error message while importing new images?
Could you please share the screenshot of the error message?
I believe the storage drive name is DataVol1 but the one in the screenshot is the Mac HD and the Photo drive with 1Tb and 50 GB space respectively.
What is the destination location you have set while importing the images?
as Homer simpson once said - Doh!
my mistake there was a quota set up on the NAS