When a Windows Server 2012 or Windows 8 based computer attempts to connect to a third-party file server that supports the SMB2 file protocol, you might see a failure to connect. You may get different error messages depending on how you’re accessing the third-party file server. These might include:

When using a DIR command with a UNC path, you get an "Invalid Signature" error.
When executing a NET USE command, you see a message saying that "System error 2148073478 has occurred."
When attempting to browse the to the UNC path, you get a message saying that "an extended error has occurred".

This behavior may be due to the "Secure Negotiate" feature added to SMB 3.0 for Windows Server 2012 and for Windows 8, which relies on the correct signing of error responses by all SMB 2 servers (including those supporting only protocol versions 2.0 and 2.1). Some third-party file servers do not respond with a signed error response causing the connection to fail.

Contact the third-party file server vendor and request an update that will allow the file server to support Windows Server 2012 and Windows 8 clients.

Enable signing on the third-party file server.

Require signing on the SMB client or the SMB server by turning on the "RequireSecuritySignature" setting. See your vendor’s documentation for instructions on setting signing to "required" on the vendor’s SMB server.

You can enable signing using PowerShell on a Windows Server 2012 or Windows 8 client with this command:

Set-SmbClientConfiguration -RequireSecuritySignature $true
Disable "Secure Negotiate" on the client.
You can do this using PowerShell on a Windows Server 2012 or Windows 8 client, using the command:
Set-ItemProperty -Path "HKLM:\SYSTEM\CurrentControlSet\Services\LanmanWorkstation\Parameters" RequireSecureNegotiate -Value 0 -Force
Note: The command as displayed above may wrap multiple lines in your web browser.