C # Error establishing connection with SQL Server

VS Version 2010

SQL version 2008

A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or could not be accessed. Verify that the instance name is correct, and that SQL Server is configured to allow remote connections. (provider:named Pipes provider, error:40-Unable to open connection to SQL Server)

SQL Server Management Studio can log on normally, but in C # it does not properly connect to SQL Server through the connection string.

You need to check the value of the server in the connection string:

Server=.; database=css;uid=sa;pwd=123456

Switch

server=jaysonchen-pc\sqlexpress;d atabase=css;uid=sa;pwd=123456

C # Error establishing connection with SQL Server