Problem resolved....
The below given command was correct I was doing a mistake that I was trying to clear the content of the readonly box before the below statement .... :) which was the culprit...
((JavascriptExecutor)Driver).executeScript("arguments[0].value=arguments[1]", Driver.findElement(By.xpath("//input[contains(@id,'startDateTimeInputDate')]")), "2012-05-28 05:33:00");
Anyhow same can also be achieved by using the web driver backed selenium....
Selenium selenium = new WebDriverBackedSelenium(driver, baseUrl);
selenium.type("//input[contains(@id,'startDateTimeInputDate')]", "2011-05-22 05:33:00");
I hope this will be helpful to others also in future...
Regards
Sandeep