Transaction is coming null Using enterrprise libary in Database.CreateConnection()

I am geeting the below error


Stack trace: at Microsoft.Practices.EnterpriseLibrary.Data.Database.PrepareCommand(DbCommand command, DbConnection connection)
at Microsoft.Practices.EnterpriseLibrary.Data.Database.PrepareCommand(DbCommand command, DbTransaction transaction)
at Microsoft.Practices.EnterpriseLibrary.Data.Database.ExecuteNonQuery(DbCommand command, DbTransaction transaction) Please find the code

try
           {
               assessmentDao.BeginTransaction();
               UpdateAssessmentStatus(Assessment);
               tempDataDao.DeleteAssessmentTemp(Assessment.ID, IdDomain, IdSubDomain);
               notInUseBL.Delete(Assessment.ID, IdDomain, IdSubDomain);
               if (!isSkip)
               {
                   foreach (AssessmentTempInfo tempData in sourceTemp)
                   {
                       tempDataDao.SaveTempData(tempData);
                   }
               }
               else
               {
                   notInUseBL.SaveOrUpdate(Assessment.ID, IdDomain, IdSubDomain);
               }
               assessmentDao.Commit();
               return true;
           }
           catch (Exception ex)
           {
               assessmentDao.Rollback();
               return false;
           }

Also find the code for begin transaction and rollback tranaction

public IDbTransaction BeginTransaction()
{
DbConnection connection = GetConnection();
_dbTransaction = connection.BeginTransaction();

//Set Transaction Indicator
IsInTransaction = true;

return _dbTransaction;
}

public void CommitTransaction()
{
_dbTransaction.Commit();
_dbConnection.Close();

_dbTransaction = null;

//Set Transaction Indicator
IsInTransaction = false;
}

public void RollbackTransaction()
{
_dbTransaction.Rollback();
_dbTransaction.Dispose();
_dbConnection.Close();

//Set Transaction Indicator
_dbTransaction = null;
IsInTransaction = false;
}

private DbConnection GetConnection()
{
_dbConnection = Database.CreateConnection();
_dbConnection.Open();
return _dbConnection;
}

#endregion

///

/// Exposing the database property
///

public Database Database
{
get
{
return DatabaseFactorySingleton.GetDatabase();
}
}

}