I have the exact same problem. I'm trying everthing since days and nothing works.
same workgroup, right IP, right name of the shared folder, the shared folder is set to my windows log in account, account name and password are also correct
=> permission denied
I don't know what i can do else...
Is there a problem with the windows features? smb1 is off
Is the windows firewall blocking it?
Is there a problem with the router? (i can easily ping from windows to pi3 kodi)
I miss those old smb1 days. plug in and it works...