Selenium Server, click by locator in ASP.NET Web Pages work unstable

Question

I have a problem when try to click for element using Selenium server method "click". The point is: sometimes some test failed, because one of element selenium doesnt fined, but in real - selenium clicked for element before the element is real displayed in page. Before the click i check isElementVisible & iselementPresent but it is doesnt help. Also i put Thread.sleep before all click.## Heading ## This is my peace of code for WaitAndClick

public void waitAndClick(String locator) throws Exception {
        long ts = System.currentTimeMillis();
        for (int second = 0;; second++) {
            if (selenium.isElementPresent(locator) == true && selenium.isVisible(locator) == true) {
            //System.out.println("click true");
                Thread.sleep(250);

                selenium.click(locator);
                 //selenium.fireEvent(locator,"click");
            //selenium.fireEvent(locator, "click");
                break;
            } else {
                //System.out.println("click false");
                Thread.sleep(100);

            }
            if (System.currentTimeMillis() - ts > 20000) {
                throw new Exception("WaitAndClick for " + locator + " out off 20 seconds");
            }
        }

    }