When you put the interval of 1 day, then you will have to have difference of at lease one day between start and end date. e.g
function TestMethod(){
var ss = SpreadsheetApp.getActiveSheet();
var startDate = new Date(2012, 10, 30);
var endDate = new Date(2012, 11, 1);
var retValue = FinanceApp.getHistoricalStockInfo('GOOG', startDate, endDate, 1);
var ret = retValue.stockInfo[0];
Logger.log(ret);
Logger.log(retValue);
}