Are you seeing the following exception message:
System.InvalidOperationException: The ConnectionString property has not been initialized. at System.Data.SqlClient.SqlConnection.PermissionDemand() at System.Data.SqlClient.SqlConnectionFactory.PermissionDemand(DbConnection outerConnection) at System.Data.ProviderBase.DbConnectionClosed.OpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory) at System.Data.SqlClient.SqlConnection.Open() at xxxxxxx in yyyyyyyy
One cause for this error is, if you try and setup a SqlConnection object with a connection string that is empty (null, nadha, nill, nothing…). So test by hard coding the connection string that you are using to create the SqlConnection. If that works – then the way that you are retrieving your connection string (web.config, custom text/xml file, etc) might be having an issue (permissions, file missing, etc).