I encounterd this error before but forgot to blog about it, when I search the internet I do find several solutions.
But what is causing this? In my case it's that I'm using a Named Instance with Dynamic IP-Port settings. The simple way to get rid of this error is by changing the Dynamic Port to the default port 1433 for all available IP entries in SQL Server Configuration Manager.
- Click Protocols for <INSTANCE>
- Right click TCP/IP and select Properties
- Remove the 0 on the TCP Dynamic Ports
- Enter the 1433 port number on the TCP Port
- Click OK and restart the SQL Server (<INSTANCE>) Service