Snapshot delete error

Brief description of the problem

I cannot delete the snapshot

Detailed step by step instructions to reproduce the problem

[write here]

Web-UI screenshot

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Error Traceback provided on the Web-UI

        Traceback (most recent call last):

File “/opt/rockstor/src/rockstor/rest_framework_custom/generic_view.py”, line 41, in _handle_exception
yield
File “/opt/rockstor/src/rockstor/storageadmin/views/snapshot.py”, line 223, in delete
self._delete_snapshot(request, sname, snap_name=snap_name)
File “/opt/rockstor/eggs/Django-1.8.16-py2.7.egg/django/utils/decorators.py”, line 145, in inner
return func(*args, **kwargs)
File “/opt/rockstor/src/rockstor/storageadmin/views/snapshot.py”, line 208, in _delete_snapshot
remove_snap(share.pool, sname, snapshot.name)
File “/opt/rockstor/src/rockstor/fs/btrfs.py”, line 589, in remove_snap
log=True)
File “/opt/rockstor/src/rockstor/system/osi.py”, line 115, in run_command
raise CommandException(cmd, out, err, rc)
CommandException: Error running a command. cmd = /sbin/btrfs subvolume delete /mnt2/Data/test1. rc = 1. stdout = [“Delete subvolume (no-commit): ‘/mnt2/Data/test1’”, ‘’]. stderr = [“ERROR: cannot delete ‘/mnt2/Data/test1’: Directory not empty”, ‘’]