https://it.awroblew.biz/windows-10-and-problems-accessing-smb-shares/

To fix this I disabled SMB 3 and enabled v1:

To disable SMBv2 and SMBv3 on the SMB client, run the following commands:

sc.exe config lanmanworkstation depend= bowser/mrxsmb10/nsi 
sc.exe config mrxsmb20 start= disabled

To enable SMBv1 on the SMB client, run the following commands:

sc.exe config lanmanworkstation depend= bowser/mrxsmb10/mrxsmb20/nsi 
sc.exe config mrxsmb10 start= auto

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https://lime-technology.com/forum/index.php?topic=37835.15

Had this problem too - it's because Win10 insists on an authenticated SMB login. You can disable it by creating the following value (a DWORD):

HKLM\SYSTEM\CurrentControlSet\Services\LanmanWorkstation\Parameters\AllowInsecureGuestAuth

Set the value to 1 , it should work straight away then.
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https://support.microsoft.com/en-us/kb/2696547

How to enable or disable SMB protocols on the SMB client
Windows Vista, Windows Server 2008, Windows 7, Windows Server 2008 R2, Windows 8, and Windows Server 2012
Note When you enable or disable SMBv2 in Windows 8 or in Windows Server 2012, SMBv3 is also enabled or disabled. This behavior occurs because these protocols share the same stack.

    To disable SMBv1 on the SMB client, run the following commands:
    sc.exe config lanmanworkstation depend= bowser/mrxsmb20/nsi
    sc.exe config mrxsmb10 start= disabled

    To enable SMBv1 on the SMB client, run the following commands:
    sc.exe config lanmanworkstation depend= bowser/mrxsmb10/mrxsmb20/nsi
    sc.exe config mrxsmb10 start= auto

    To disable SMBv2 and SMBv3 on the SMB client, run the following commands:
    sc.exe config lanmanworkstation depend= bowser/mrxsmb10/nsi
    sc.exe config mrxsmb20 start= disabled

    To enable SMBv2 and SMBv3 on the SMB client, run the following commands:
    sc.exe config lanmanworkstation depend= bowser/mrxsmb10/mrxsmb20/nsi
    sc.exe config mrxsmb20 start= auto
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Windows 8 and Windows Server 2012
Windows 8 and Windows Server 2012 introduce the new Set-SMBServerConfiguration Windows PowerShell cmdlet. The cmdlet enables you to enable or disable the SMBv1, SMBv2, and SMBv3 protocols on the server component.

Notes When you enable or disable SMBv2 in Windows 8 or in Windows Server 2012, SMBv3 is also enabled or disabled. This behavior occurs because these protocols share the same stack.

You do not have to restart the computer after you run the Set-SMBServerConfiguration cmdlet.

    To obtain the current state of the SMB server protocol configuration, run the following cmdlet:
    Get-SmbServerConfiguration | Select EnableSMB1Protocol, EnableSMB2Protocol

    To disable SMBv1 on the SMB server, run the following cmdlet:
    Set-SmbServerConfiguration -EnableSMB1Protocol $false

    To disable SMBv2 and SMBv3 on the SMB server, run the following cmdlet:
    Set-SmbServerConfiguration -EnableSMB2Protocol $false

    To enable SMBv1 on the SMB server, run the following cmdlet:
    Set-SmbServerConfiguration -EnableSMB1Protocol $true

    To enable SMBv2 and SMBv3 on the SMB server, run the following cmdlet:
    Set-SmbServerConfiguration -EnableSMB2Protocol $true