На строчке System.Data.SqlClient.SqlDataReader reader=myCommand.ExecuteReader(); вылазит
эксепшн
An unhandled exception of type 'System.Data.SqlClient.SqlException' occurred in system.data.dll

Additional information: System error.

Где грабли?

private void SCommand(string ConnectionString)
{
string command="Select * from strat";
System.Data.SqlClient.SqlConnection myConnection = new System.Data.SqlClient.SqlConnection(ConnectionString);
MessageBox.Show(myConnection.State.ToString());
myConnection.Open();
MessageBox.Show(myConnection.State.ToString());

int n=0;
System.Data.SqlClient.SqlCommand myCommand = new System.Data.SqlClient.SqlCommand(command, myConnection);
MessageBox.Show(myCommand.Connection.State.ToString());
System.Data.SqlClient.SqlDataReader reader=myCommand.ExecuteReader();
n=reader.FieldCount;
for(int i=0;i<n;i++)
{
MessageBox.Show(reader.GetString(i));
}

}