Can't delete an unused ReadyDR share

Hi,

I can't delete an old ReadyNas DR share I set up while testiing months ago. I get the following error in the web interface.

"Could not delete share due to snapshot deleteion failure, Code 1004030000"

I have tried  updating to 6.7.5 and so rebooted.

I have downloaded the logs from the NAS and the following looks like the issue

Jun 26 10:38:47 NAS01 snapperd[3632]: Snapper delete-config
Jun 26 10:38:47 NAS01 snapperd[3632]: loading 208 failed
Jun 26 10:38:47 NAS01 snapperd[3632]: delete subvolume failed, ioctl(BTRFS_IOC_SNAP_DESTROY) failed, errno:39 (Directory not empty)
Jun 26 10:38:47 NAS01 snapperd[3632]: THROW: deleting btrfs snapshot failed
Jun 26 10:38:47 NAS01 snapperd[3632]: THROW: deleting snapshot failed
Jun 26 10:38:47 NAS01 snapperd[3632]: CAUGHT: deleting snapshot failed

Any ideas how to remove it ?

Thanks

Phil