I get the error message ‘Keyword not supported: ‘provider”, when using Sql Server why?

If you are using SqlConnection then the connection string should be as follows:

server=localhost;uid=sa;password=;database=northwind
i.e
server=<yourservername>;uid=<youruid>;password=<yourpassword>;database=<yourdbName>'

For SqlConnection we do not provide a Provider . Provider is used in cases where OleDbConnection is used.