Getting Error while creating a connection with oracle database.

Please Help... Y i am getting error i have no idea. Yesterday it was working fine. Now it is showing error.
Error:  An invalid or incomplete configuration was used while creating a SessionFactory. Check PotentialReasons collection, and InnerException for more detail.
1)  public static ISessionFactory SessionFactory
{
get
{
if (_sessionFactory == null)
InitializeSessionFactory(); return _sessionFactory; } }

2)
// using Oracle string
public static void InitializeSessionFactory() {
_sessionFactory = Fluently.Configure()
.Database(OracleClientConfiguration.Oracle10 .ConnectionString( @"DATA SOURCE=XE;PERSIST SECURITY INFO=True;USER ID=system;Password=system;") // Modify your ConnectionString
.ShowSql()
)
.Mappings(m => m.FluentMappings .AddFromAssemblyOf<Userl ...