A stacktrace showing the issue on Windows XP SP3, Selenium 2.21.0, Internet Explorer
8, searching for an element by XPath (so no CSS selector as OP stated):

Error: org.openqa.selenium.WebDriverException (Unable to find element with xpath ==
//*[contains(text(),'Align') or contains(@value,'Align')] (WARNING: The server did
not provide any stacktrace information)
Command duration or timeout: 688 milliseconds
Build info: version: '2.2.1', revision: '16551', time: '2012-04-11 21:42:35'
System info: os.name: 'Windows XP', os.arch: 'x86', os.version: '5.1', java.version:
'1.6.0_22'
Driver info: driver.version: RemoteWebDriver)

sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
java.lang.reflect.Constructor.newInstance(Unknown Source)
org.openqa.selenium.remote.ErrorHandler.createThrowable(ErrorHandler.java:175)
org.openqa.selenium.remote.ErrorHandler.throwIfResponseFailed(ErrorHandler.java:128)
org.openqa.selenium.remote.RemoteWebDriver.execute(RemoteWebDriver.java:459)
org.openqa.selenium.remote.RemoteWebDriver.findElement(RemoteWebDriver.java:227)
org.openqa.selenium.remote.RemoteWebDriver.findElementByXPath(RemoteWebDriver.java:312)
org.openqa.selenium.By$ByXPath.findElement(By.java:344)
org.openqa.selenium.remote.RemoteWebDriver.findElement(RemoteWebDriver.java:219)

Please provide a reduced test case (WebDriver code with accompanying HTML demo page)
to reproduce the issue.

This is not a common issue, it can be related to your page or the locator you use.
Here is an example that shows that selenium throws a valid exception:

RemoteWebDriver driver = new InternetExplorerDriver();
driver.get("http://localhost/");
driver.findElement(By.cssSelector("test"));

--->

Exception in thread "main" org.openqa.selenium.NoSuchElementException: Unable to find
element with css selector == test (WARNING: The server did not provide any
 stacktrace information)
Command duration or timeout: 304 milliseconds
For documentation on this error, please visit: http://seleniumhq.org/exceptions/no_such_element.html
Build info: version: '2.19.0', revision: '15849', time: '2012-02-08 16:10:57'
System info: os.name: 'Windows 7', os.arch: 'amd64', os.version: '6.1', java.version:
'1.6.0_30'
Driver info: driver.version: RemoteWebDriver
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
    at java.lang.reflect.Constructor.newInstance(Unknown Source)
    at org.openqa.selenium.remote.ErrorHandler.createThrowable(ErrorHandler.java:170)
    at org.openqa.selenium.remote.ErrorHandler.throwIfResponseFailed(ErrorHandler.java:123)
    at org.openqa.selenium.remote.RemoteWebDriver.execute(RemoteWebDriver.java:439)
    at org.openqa.selenium.remote.RemoteWebDriver.findElement(RemoteWebDriver.java:226)
    at org.openqa.selenium.remote.RemoteWebDriver.findElementByCssSelector(RemoteWebDriver.java:291)
    at org.openqa.selenium.By$ByCssSelector.findElement(By.java:407)
    at org.openqa.selenium.remote.RemoteWebDriver.findElement(RemoteWebDriver.java:218)
    at org.openqa.selenium.example.Sample.main(Sample.java:50)

That's the pickle - it happens only sometimes (but at the same place, that's true) and
I can't get my hands around it. I'll try to reduce the test case in the upcoming days.
Thanks for looking at it, anyway!
(Also, could you please rename the topic header, as I proved that it happens with XPath
selectors, too?)

To the OP: What did precede the failing call? In our case, it usually is async redirect
that hasn't completed yet...

I also managed to reproduce with an xpath selector against the same element as I originally
saw the problem with the css selector some time ago.
I'm testing a proprietary system and can't just paste the code I'm afraid and it isn't
easy to just isolate the offending element. 

I've faced the same problem with IE 9. All tests were executed, browser redirected,
but all of them failed because of the same Exception as is mentioned here (org.openqa.selenium.WebDriverException
(Unable to find element with xpath == //*[contains(text(),'some text')). The problem
was, that JavaScript was disabled in browser. If you are using IE 9 (don't know if
developers tools are in previous versions too), try to press F12 and check if in the
pop-up developer tools window is unchecked option Disabled > Script.

I'm facing the same problem with IE 8. Please find the details below:
Build info: version: '2.24.1', revision: '17205', time: '2012-06-19 17:28:14'
System info: os.name: 'Windows 7', os.arch: 'x86', os.version: '6.1', java.version:
'1.6.0_25'
Driver info: driver.version: RemoteWebDriver

The same code is performing well in a different system with same configuration.

What we really need is a reproduction case, not configuration details.

I've provided a sample that shows this feature works *in general* (see comment 3).

Obviousely there is an edge case where it does not work, and we need to catch it.

The attached testcase reproduces the issue.

This also reproduces bug http://code.google.com/p/selenium/issues/detail?id=3800 which
is the same issue with the difference of using findElement instead of findElements


The issue seems to be that the current page changes while findElement(s) is running.

I'm also getting JavaScript errors in the JS console when this happens:


Message: Can't execute code from a freed script
Line: 1
Char: 72
Code: 0
URI: http://xx.xx.xx.xx/xxxx

Since bug 3800 is (hopefully) fixed, is this fixed, too? I can't reproduce the bug via
the testcase in comment #10 (though I haven't really been able to reproduce it with
an old version, either).

Hi!

At this moment at my machine (Win7 x64) i see:
* 38 errors with incorrect exception types for local drivers (4 from 5, Safari is not
supported yet)
* 44 errors with incorrect exception types for remote drivers (5 from 5)

Error means that type of raised exception is out of list (NoSuchElementException, NoSuchWindowException,
InvalidSelectorException).
This list is made from WD protocol (with one fix - XpathInvalidError replaced by InvalidSelectorException).

NOTE: this is for python binding. I think for another bindings list of errors will
be different.
It would be great if someone create tests for each binding using my scripts as examples.
:)

Selenium version is 2.31. Chromedriver and IEDriverServer are last from Downloads.
Browsers list:
* IE 9.0.xxx x32
* FF 19.0.2
* Chrome 25.0.xxx
* Opera 12.14
* Safari 5.1.7

The found errors are attached as 2 files: remote_errors and local_errors. 2 test scripts
are attached too.

Format of each error (2 variants for single element and multiple elements differs only
by S):

<driver id>: Non correct exception <exception type>()(<exception message>) is occured
during search element by: (<selector type>, <selector value>)
<driver id>: Non correct exception <exception type>()(<exception message>) is occured
during search elements by: (<selector type>, <selector value>)

IE and Firefox are green in the trunk.

Opera (deprecated) and Chrome have failing tests, see @Ignore annotations in ElementFindingTest