Symptom

This is what you see when you try to go to any \\something network share:

\\something is not accessible. You might not have permission to use this network resource. Contact the administrator of this server to find out if you have access permissions. The account is not authorized to log in from this station.

Solution

Fire up the registry editor (regedit). Navigate to:

HKLM\SYSTEM\CurrentControlSet\Services\LanmanWorkstation\Parameters

Here, you will need to create a new parameter (32-bit DWORD). Right-click:

Then, name it AllowInsecureGuestAuth and assign it a value of 1.

The hive should look thusly:

And you're done. Reboot, and enjoy your network access.

 https://www.dedoimedo.com/computers/windows-10-network-share-access.html

And more reference:

https://blog.xuite.net/yh96301/blog/548723165-Windows+10+%E5%AD%98%E5%8F%96%E7%B6%B2%E5%9F%9F%E5%85%A7%E5%88%86%E4%BA%AB%E7%9A%84%E8%B3%87%E6%96%99

Mapped Network Drives don’t work in Windows 10 v2004

Windows Registry Editor Version 5.00
; Change Extension's File Type
[HKEY_CURRENT_USER\Software\Classes\.jpg]
@="PhotoViewer.FileAssoc.Tiff"
; Change Extension's File Type
[HKEY_CURRENT_USER\Software\Classes\.jpeg]
@="PhotoViewer.FileAssoc.Tiff"
; Change Extension's File Type
[HKEY_CURRENT_USER\Software\Classes\.gif]
@="PhotoViewer.FileAssoc.Tiff"
; Change Extension's File Type
[HKEY_CURRENT_USER\Software\Classes\.png]
@="PhotoViewer.FileAssoc.Tiff"
; Change Extension's File Type
[HKEY_CURRENT_USER\Software\Classes\.bmp]
@="PhotoViewer.FileAssoc.Tiff"
; Change Extension's File Type
[HKEY_CURRENT_USER\Software\Classes\.tiff]
@="PhotoViewer.FileAssoc.Tiff"
; Change Extension's File Type
[HKEY_CURRENT_USER\Software\Classes\.ico]
@="PhotoViewer.FileAssoc.Tiff"

.....................................

Win7_Photo_Viewer.reg

1. reg add HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\system /v LocalAccountTokenFilterPolicy /t REG_DWORD /d 1 /f 
2. Reboot the PC.

Method 1: Use Registry Editor

Domain controller locator configuration for Windows XP Professional and later versions of Windows

1. Click Start, click Run, type regedit, and then click OK.
2. Locate and then click the following subkey:
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Netlogon\Parameters
3. In the details pane, locate the AllowSingleLabelDnsDomain entry. If the AllowSingleLabelDnsDomain entry does not exist, follow these steps:
   1. On the Edit menu, point to New, and then click DWORD Value.
   2. Type AllowSingleLabelDnsDomain as the entry name, and then press ENTER.
4. Double-click the AllowSingleLabelDnsDomain entry.
5. In the Value data box, type 1, and then click OK.
6. Exit Registry Editor.

DNS client configuration

1. Click Start, click Run, type regedit, and then click OK.
2. Locate and then click the following subkey:
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\DnsCache\Parameters
3. In the details pane, locate the UpdateTopLevelDomainZones entry. If the UpdateTopLevelDomainZones entry does not exist, follow these steps:
   1. On the Edit menu, point to New, and then click DWORD Value.
   2. Type UpdateTopLevelDomainZones as the entry name, and then press ENTER.
4. Double-click the UpdateTopLevelDomainZones entry.
5. In the Value data box, type 1, and then click OK.
6. Exit Registry Editor.

• For Windows Server 2003 and later versions, the UpdateTopLevelDomainZones entry has moved to the following registry subkey:
  HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows NT\DNSClient
• On a Microsoft Windows 2000 SP4-based domain controller, the computer will report the following name registration error in the System event log if the UpdateTopLevelDomainZones setting is not enabled:
• On a Windows 2000 SP4-based domain controller, you must restart your computer after you add the UpdateTopLevelDomainZones setting.