Today when opening a project in Visual Studio 2015 I recieved the following error:
—————————Microsoft Visual Studio —————————
A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified)
————————— OK —————————
The problem seemed to be some old data connections in server explorer.
By deleting all the connections and letting Visual studio create them again the error disappeared. 