If you get the following error:

Could not connect to server 172.16.1.16
Connection failed: NT_STATUS_ACCESS_DENIED
Could not connect to server 172.16.1.16
Connection failed: NT_STATUS_ACCESS_DENIED

with this command line

net rpc -S 172.16.1.16 -U administrator%password shutdown -t 1 -f

You have to add the following line to /etc/samba/smb.conf

client ipc signing = auto