SMB signing can be enabled in Windows by setting the registry key “RequireSecuritySignature” to 1. After SMB signing is enabled, Windows is unable to connect to SMB shares on a QNAP NAS.
To work around this problem, open Powershell on the Windows client and run the following command to disable “secure negotiate”:
"HKLM:\SYSTEM\CurrentControlSet\Services\LanmanWorkstation\Parameters" RequireSecureNegotiate -Value 0 –Force
For more information, see: https://support.microsoft.com/en-us/help/2686098/-system-error-2148073478,-extended-error,-or-invalid-signature-error-message-on-smb-connections-in-windows-server-2012-or-windows-8