probleme de convertion de type dans le résultat d'une requete

private: System::Void button1_Click(System::Object^  sender, System::EventArgs^  e) {
			l7=double::Parse(this->label15->Text);
			l8=double::Parse(this->label16->Text);
		    
			 foundJustUsed=true;
             try
                      {
                if (!textBox7->Text->Equals( String::Empty )&&(this->dateTimePicker1->Value<=this->dateTimePicker2->Value  ))
                           {
                            String ^myQuery = "SELECT code_emp_accés,SUM(horaire1_jour) FROM accés WHERE  code_emp_accés='"+textBox7->Text+"'   AND (jour_accés between '"+l7+"' AND'"+l8+"') GROUP By code_emp_accés";
                           
							OleDbCommand ^myCommand = gcnew OleDbCommand(myQuery, oleDbConnection1);
                              OleDbDataReader ^myReader; //works
                              myReader = myCommand->ExecuteReader();
							  myReader->Read();
							myReader->GetString(0)->ToString();
						this->textBox3->Text=myReader->GetDouble(1).ToString();
	                   
							  myReader->Close();
							    MessageBox::Show("\r\nok\r\n")  ;
					 
				} // end if
                else
                 
                 MessageBox::Show("\r\nentrez les renseignement nécessaire\r\n") ;
			
               } // end try
               catch ( Exception ^Exception ) { //catches all errors
                  MessageBox::Show( Exception->Message, "employé non trouvé",
                     MessageBoxButtons::OK, MessageBoxIcon::Error );
               } // end catch
                       
		 }