Recently a customer changed the password on their server in a peer to peer network. As a result, no-one could access the shared folders.
The interesting part is one program, that has a database, on the server worked just fine, while another would error out.
If they tried to navigate to the server via “Network” it popped up asking for a username and password.

If the server Administrator account was entered, they could log on all week. The next Monday, the failures would repeat.
On the server File Sharing was turned on, it was shared to “Everyone” and “Authenticated Users” both with full permissions. Under “Security” the “Everyone” and “Authenticated Users” had full permissions.
In other words, all normal sharing settings were correct.
The individual computers have different users which were NOT on the server as users. After all that is what the “Everyone” and “Authenticated Users” accounts were for. Also, it had on this server since it was installed December 2017.
The computers were Windows 7, 8 and 10. The server is Windows Server 2016 Standard.

It turned out that on each PC under “Credential Manager” and under “Windows Credentials” was “server”. I had to change the password there.

If you are having this issue you can update your credentials.
In Windows 10 open “Settings”, type in “Credential” in the search box and select Credential Manager from the list.

You will have a choice of ‘Web Credentials’ or ‘Windows Credentials’. Click on ‘Windows Credentials’.

Below it will appear the list of your computers saved credentials. You can click on the arrow next to the credential to edit or remove them.

Edit pops up a new window where you can make the needed changes.

That turned out to be all that was needed to fix the situation. Hopefully this will help you save some time and stress.

Until we meet again, have a virus free week.