The SMB Protocol
Windows uses the SMB protocol for LANs, starting with SMB1. However, there were security holes discovered with SMB1. As a result newer versions of Windows mostly use SMB2/3, and often will not connect to SMB1.
However, many computers have been migrated from earlier versions of Windows and as such have SMB1 enabled. The fix for many connection problems on a LAN is simple. Disable SMB1 and enable SMB2/3.
Start PowerShell as Administrator, then enter the following as 2 separate commands:
Set-SmbServerConfiguration -EnableSMB2Protocol $true
Set-SmbServerConfiguration -EnableSMB1Protocol $false
reboot your computer to be sure, and the problem will be solved. To check the status of SMB, again using PowerShell, enter the following as 2 separate commands:
Get-SmbServerConfiguration | Select EnableSMB1Protocol
Get-SmbServerConfiguration | Select EnableSMB2Protocol