When creating a new Knowledge Base with its corresponding database, the following errors may occur if the database connection was incorrectly installed.

To solve them, follow the steps below:

1- Open the Internet Information Services Manager.



Once inside it, click on “Application Pools.”




Add the corresponding user(s) according to the error displayed.
To do so, select Add Application Pool (in the panel on the right) and enter the users:

ASP.NET v4.0
Classic .NET AppPool




They must look as shown below:



2 – Configuring users at SQLServer level. 

Open Microsoft SQL Server Management Studio:



Create the corresponding users.

To do so, open the folder Security -> Login, right-click and select New Login.




Enter the same username as you did in the IIS, in this case with the full path:
IIS AppPool\ASP.NET v4.0
IIS AppPool\Classic .NET AppPool




They must look as shown below: