You have to provide a data provider such as "Provider=SQLOLEDB;" in your connection string. SqlConnection doesn't allow you to use a provider in the connection string, but the server control expects one since it relies on a generic OleDb connection rather than a specific SqlConnection.

Therefore you should change your code as:

Dim cnExchange As New OleDb.OleDbConnection(ConfigurationSettings.AppSettings("connectionString"))

and set a provider in your connection string in the web.config file as:

<add key="connectionString" value="Provider=SQLOLEDB;User ID=sa;Password=sa;Initial Catalog=YourDatabaseName;Data Source=YourServerName;" />