Issue:
You receive the following error when trying to login to Forecast 5.
Forecast 5 cannot continue because of an exception occurred.
SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified.

Cause:
This error indicates that Forecast 5 is unable to connect to the currently specified database or cannot see the SQL Server.
Solution:
If Forecast 5 cannot find SQL Server or database, there are a few causes:
this article from Microsoft gives you the full detail.
1. SQL server name in the config file is misspelled or incorrect.
- Ensure you have entered the correct name.
2. The Instance name is incorrect or does not exist.
- Ensure that the instance is correct and valid.
3. The server is not reachable.
- Ensure that Named Pipes, TCP/IP and SQL Brower service have been enabled and are running. Best to restart the SQL Server in this case.
- If this does not work, try Ping the server. If this fails, you need to look into the server set up.
4. The Firewall on the server is enabled.
- This needs to be disabled.
If the SQL Server is not running, open the windows menu and search for Services/Local Services:

Scroll down until you find your SQL Server and make sure that its status is Running:

If it is showing as Stopped select your SQL server, right click on it and select Start.