This problem is caused by the „Secure Negotiate“ feature that was added to SMB 3.0 for Windows Server 2012 R2 – this feature depends upon the correct signing of error responses by all SMBv2 servers including servers that support only protocol versions 2.0 and 2.1 – some third-party file servers (e.g. older samba versions) do not return a signed error response
You can disable the „Secure Negotiate“ feature by using PowerShell on a Windows Server 2012 R2