1. If Computer Configuration > Administrative Templates > Network > Lanman Workstation > Enable insecure guest logons shows "Enabled" but it isn't working, continue
2. Open the registry editor and go to Computer\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\LanmanWorkstation\Parameters
3. Double-click on AllowInsecureGuestAuth
4. Under "Value data:", change it from 0 to 1
Describing what I did troubleshooting-wise (not that it matters, but maybe it'll help someone):
I updated my Windows 10 Education to version 2004 yesterday and was no longer able to access my SMB shares (was working fine before Windows update).
I could see them, but double-clicking on my server name in Windows Explorer under Network gave me the generic can't access error. Luckily (because it helped me google my problem) I had pinned some folders in it, and trying to access those gave me the popup pictured in that preview/thread saying:
"You can't access this shared folder because your organization's security policies block unauthenticated guest access. These policies help protect your PC from unsafe or malicious devices on the network."
I was confused because my group policy under:
Computer Configuration > Administrative Templates > Network > Lanman Workstation > Enable insecure guest logons
showed "Enabled". Toggling this back and forth and restarting my PC didn't fix anything.
My unRAID server SMB settings had enabled for workgroup, enable NetBIOS to yes, and enable WSD to yes. My workgroup under those SMB settings matched with my PC, I even retyped them in holding down shift to capitalize just in case. Local master was set to yes, and I also downloaded the Dynamix Local Master plugin to check for me and it verified that yes, my unRAID server was indeed the current local master. Still not working.
to SMB Extras and saw in my syslog that my PC was trying to send my local user to access the SMB shares (which are set to public) with errors along the lines of:
FAILED with error NT_STATUS_NO_SUCH_USER, authoritative=1
and that I was trying to use SMBv2
In the end, I found the solution in the linked thread to do this:
1. Open the registry editor and go to Computer\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\LanmanWorkstation\Parameters
2. Double-click on AllowInsecureGuestAuth
3. Under "Value data:", change it from 0 to 1