USB Drive attached to Airport Extreme not showing(?)

If I connect the drive directly to a computer via USB the share is there, to the airport, the share isn't there. I ran disk utility when directly connected, no problems.

Airport Utility shows the share as being there, correct free space, etc.. But on my Macbook /Volumes doesn't show any trace of it, finder shows nothing.

I've rebooted both router and computer.

I've used this drive for a long time and I've never had this happen, and I upgraded to 10.10.5 recently... can't see that as being the problem. The device is set to secure shared disks with device password, no change there. (Disks?).

Help?