Here is a test that passes for me (Win7 x64, FF 5.0):

        [TestMethod]
        public void TestMethod1()
        {
            IWebDriver browser = new RemoteWebDriver(new Uri("http://localhost:4444/wd/hub"),
DesiredCapabilities.Firefox());
            browser.Url = "http://jqueryui.com/demos/selectable/";

            IList<IWebElement> elements = browser.FindElements(By.CssSelector("ol#selectable
li"));

            Actions a = new Actions(browser);
            IAction x = a.KeyDown(Keys.Shift)
                  .MoveToElement(elements[0])
                  .Click()
                  .MoveToElement(elements[1])
                  .Click()
                  .KeyUp(Keys.Shift)
                  .Build();
            x.Perform();

            browser.Quit();
        }

Server log is:

20:31:45.294 INFO - Executing: [new session: {platform=ANY, browserName=firefox, version=}]
at URL: /session)
20:31:52.099 INFO - Done: /session
20:31:52.102 INFO - Executing: org.openqa.selenium.remote.server.handler.GetSessionCapabilities@7a4fe91e
at URL: /sessio
n/1321378290834)
20:31:52.102 INFO - Done: /session/1321378290834
20:31:52.140 INFO - Executing: [get: http://jqueryui.com/demos/selectable/] at URL:
/session/1321378290834/url)
20:31:57.627 INFO - Done: /session/1321378290834/url
20:31:57.631 INFO - Executing: [find elements: By.selector: ol#selectable li] at URL:
/session/1321378290834/elements)
20:31:57.657 INFO - Done: /session/1321378290834/elements
20:31:57.664 INFO - Executing: [send keys to active: ?] at URL: /session/1321378290834/keys)
20:31:57.674 INFO - Done: /session/1321378290834/keys
20:31:57.677 INFO - Executing: [mousemove: 0 false] at URL: /session/1321378290834/moveto)
20:31:57.865 INFO - Done: /session/1321378290834/moveto
20:31:57.868 INFO - Executing: [click: nothing] at URL: /session/1321378290834/click)
20:31:57.887 INFO - Done: /session/1321378290834/click
20:31:57.889 INFO - Executing: [mousemove: 1 false] at URL: /session/1321378290834/moveto)
20:31:58.020 INFO - Done: /session/1321378290834/moveto
20:31:58.022 INFO - Executing: [click: nothing] at URL: /session/1321378290834/click)
20:31:58.033 INFO - Done: /session/1321378290834/click
20:31:58.035 INFO - Executing: [send keys to active: ?] at URL: /session/1321378290834/keys)
20:31:58.041 INFO - Done: /session/1321378290834/keys
20:31:58.042 INFO - Executing: [delete session: 1321378290834] at URL: /session/1321378290834)
20:31:59.106 INFO - Done: /session/1321378290834

So, you probably have something special on your page that causes the issue.

Could you please provide a reduced test case that includes a sample page (HTML, CSS,
JS) and the test code to reproduce the issue?

When I use Your code, I also have Unexpected error.

09:34:34.959 INFO - Executing: [new session: {platform=ANY, browserName=firefox, version=}]
at URL: /session)
09:34:39.300 INFO - Executing: [null, newSession {"desiredCapabilities":"Capabilities
[{platform=ANY, browserName=firefox, version=}]"}]
09:34:39.872 INFO - Done: /session
09:34:39.910 INFO - Executing: org.openqa.selenium.remote.server.handler.GetSessionCapabilities@fc8fb4b
at URL: /session/1325234053523)
09:34:39.911 INFO - Done: /session/1325234053523
09:34:39.981 INFO - Executing: [get: http://jqueryui.com/demos/selectable/] at URL:
/session/1325234053523/url)
09:34:39.982 INFO - Executing: [ff45ac3b-10e8-4192-8da4-abe5f75d3962, get {"url":"http://jqueryui.com/demos/selectable/"}]
09:34:43.684 INFO - Done: /session/1325234053523/url
09:34:43.689 INFO - Executing: [find elements: By.selector: ol#selectable li] at URL:
/session/1325234053523/elements)
09:34:43.690 INFO - Executing: [ff45ac3b-10e8-4192-8da4-abe5f75d3962, findElements
{"using":"css selector","value":"ol#selectable li"}]
09:34:43.720 INFO - Done: /session/1325234053523/elements

Please can you try on a different machine and see if that is still an issue

ok, in new version of selenium I don't have error, but only one element is selected,
like the shift button does not work...

I try your code on page: http://jqueryui.com/demos/selectable/

Hi!

Yes, it selects only one element - manually it does the same.
For selecting multiple elements use CTRL+click.

From my point of view, this issue is fixed.

ok, in my opinion problem is sloved