Recent updates to the Windows 10 operating system have rendered SMB guess access disabled by default. While this is a good thing, there are situations in certain office settings where guest access to some office shares is still in use. As a short-term fix, the following can be used to gain users access to the resource while working to provide a long-term, secure solution.
The issue seems to center around the fact that there are two separate settings that need enabled for guest access to work: one is a group policy setting and the other is a registry setting.
Group Policy Setting
1. Open group policy editor: gpedit.msc via control panel or the RUN window
2. In Group Policy Editor, select:
Computer Configuration -> Administrative Templates -> Network -> Lanman Workstation
3. Right-click Enable insecure guest logons and select Edit
4. Select Enabled and select OK
Registry Setting
1. Open registry policy editor: regedit.msc in the RUN window
2. In Registry Editor, open [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\LanmanWorkstation\Parameters]
3. Right-click AllowInsecureGuestAuth [dword] and select Modify...
4. Enter a value of 1 and select OK
More information can be found in the Microsoft document found here