I'm seeing this as well. I have some code asserting that a given text is present for
a "By" locator. Before I attempt to retrieve the text, i use a "wait.until" block,
just to make sure.

As the OP, I'm also seeing this with By.xpath expressions only and the error is thrown
in the "findElement" part of the ExpectedCondition.

I think I've seen this pretty consistenly on a test for a given page title using a
By.xpath("//head/title") locator on a page, that is generated really fast.

I'm also hitting this issue on Firefox5/Linux for very simple XPath statements such
as 

//*[@class='access-denied']

id("modalframe-container")

After googling a little more for my issue, i realize it may actually be an error related
to using the redirect-after-post pattern/a race between get() and findElement()

And I am using capybara, using this:

      should "only see the 'comment' action button" do
        assert has_selector?('#comment_button')
        assert has_selector?('#i_want_this_too_button')
        assert has_selector?('#make_offer_button')
      end

      should "see links to view offers" do
        assert has_selector?('.view_offer')
      end

and I get those errors every other time I run the tests..  It's proving to be very
frustrating!

FYI: This post (http://carol-nichols.com/2011/07/seleniumwebdrivererrorunhandlederror-ns_error_illegal_value/)
mentions a workaround if you're using Capybara.

Issue 2287 has been merged into this issue.

Most frameworks using WebDriver as a building block (Capybara, watir-webdriver) rely
heavily on XPath, so would be good to have this fixed by (at least) 2.6. 

We're seeing the same problem when running capybara and selenium-webdriver and any kind
of parallel testing tool (parallel_test, specjour) even though it runs perfectly when
running it on a single core.

I've managed to reproduced it somewhat consistently, by running the native test suite
on Linux with Firefox 6 (on Gnome, *not* xvfb / xvnc). The last test before the failing
one is testShouldNotHangIfDocumentOpenCallIsNeverFollowedByDocumentCloseCall:

Testcase: testShouldNotHangIfDocumentOpenCallIsNeverFollowedByDocumentCloseCall took
0.035 sec
Testcase: testShouldReturnNullWhenGettingTheValueOfAnAttributeThatIsNotListed took
0.031 sec
        Caused an ERROR
The given selector /html is either invalid or does not result in a WebElement. The
following error occurred:
[InvalidSelectorError] Unable to locate an element with the xpath expression /html
because of the following error:
[Exception... "Component returned failure code: 0x80070057 (NS_ERROR_ILLEGAL_VALUE)
[nsIDOMXPathEvaluator.createNSResolver]"  nsresult: "0x80070057 (NS_ERROR_ILLEGAL_VALUE)"
 location: "JS frame :
: resource://fxdriver/modules/atoms.js :: <TOP_LEVEL> :: line 2382"  data: no]; duration
or timeout: 22 milliseconds
For documentation on this error, please visit: http://seleniumhq.org/exceptions/invalid_selector_exception.html
Build info: version: '2.7.0', revision: '13884', time: '2011-09-21 13:55:08'
System info: os.name: 'Linux', os.arch: 'i386', os.version: '2.6.38.8-gg621', java.version:
'1.6.0-google-v4'
Driver info: driver.version: RemoteWebDriver
org.openqa.selenium.InvalidSelectorException: The given selector /html is either invalid
or does not result in a WebElement. The following error occurred:
[InvalidSelectorError] Unable to locate an element with the xpath expression /html
because of the following error:
[Exception... "Component returned failure code: 0x80070057 (NS_ERROR_ILLEGAL_VALUE)
[nsIDOMXPathEvaluator.createNSResolver]"  nsresult: "0x80070057 (NS_ERROR_ILLEGAL_VALUE)"
 location: "JS frame :: resource://fxdriver/modules/atoms.js :: <TOP_LEVEL> :: line
2382"  data: no]; duration or timeout: 22 milliseconds
For documentation on this error, please visit: http://seleniumhq.org/exceptions/invalid_selector_exception.html
Build info: version: '2.7.0', revision: '13884', time: '2011-09-21 13:55:08'
System info: os.name: 'Linux', os.arch: 'i386', os.version: '2.6.38.8-gg621', java.version:
'1.6.0-google-v4'
Driver info: driver.version: RemoteWebDriver

just want to chime in - we're seeing the same thing: seems to be reasonably consistent
when we pop a modal overlay on page load and try to confirm the existence of some text
in the overlay:


 Failure/Error: page.should have_content "Success! Your item is now listed."
     Selenium::WebDriver::Error::InvalidSelectorError:
       The given selector "./descendant-or-self::*[contains(normalize-space(.), 'Success!
Your item is now listed.')] is either invalid or does not resultin a Webelement. The
following error occurred:
       [InvalidSelectorError] Unable to locate elements with the xpath expression ./descendant-or-self::*[contains(normalize-space(.),
'Success! Your item is now listed.')] because of the following error:
       [Exception... "Component returned failure code: 0x80070057 (NS_ERROR_ILLEGAL_VALUE)
[nsIDOMXPathEvaluator.createNSResolver]"  nsresult: "0x80070057 (NS_ERROR_ILLEGAL_VALUE)"
 location: "JS frame :: resource://fxdriver/modules/atoms.js :: <TOP_LEVEL> :: line
2360"  data: no]
     # [remote server] file:///var/folders/ll/0csh8smd025d9mgh2nf842400000gn/T/webdriver-profile20110923-3328-9h1oht/extensions/fxdriver@googlecode.com/components/driver-component.js
-> file:///var/folders/ll/0csh8smd025d9mgh2nf842400000gn/T/webdriver-profile20110923-3328-9h1oht/extensions/fxdriver@googlecode.com/components/firefoxDriver.js:466:in
`unknown'
     # [remote server] file:///var/folders/ll/0csh8smd025d9mgh2nf842400000gn/T/webdriver-profile20110923-3328-9h1oht/extensions/fxdriver@googlecode.com/components/driver-component.js
-> file:///var/folders/ll/0csh8smd025d9mgh2nf842400000gn/T/webdriver-profile20110923-3328-9h1oht/extensions/fxdriver@googlecode.com/components/firefoxDriver.js:507:in
`unknown'
     # [remote server] file:///var/folders/ll/0csh8smd025d9mgh2nf842400000gn/T/webdriver-profile20110923-3328-9h1oht/extensions/fxdriver@googlecode.com/components/nsCommandProcessor.js:306:in
`unknown'
     # [remote server] file:///var/folders/ll/0csh8smd025d9mgh2nf842400000gn/T/webdriver-profile20110923-3328-9h1oht/extensions/fxdriver@googlecode.com/components/nsCommandProcessor.js:320:in
`unknown'
     # [remote server] file:///var/folders/ll/0csh8smd025d9mgh2nf842400000gn/T/webdriver-profile20110923-3328-9h1oht/extensions/fxdriver@googlecode.com/components/nsCommandProcessor.js:197:in
`unknown'
     # (eval):2:in `has_content?'

See also revision 13403

I can trigger this error fairly consistently by running a Selenium wait_until on a page
with a meta Refresh=1 header, meaning it reloads every second.  If the wait_until check
(every 0.05s) coincides with a page reload, it goes boom.

Could you post a code example?

Is this issue related to a specific version?

The meta refresh trick will trigger issue 1438 for me, but not this one. I've added
it as an example there.

I get this same error about 35% of the time on certain tests runs.  It's not 100% repeatable,
and will only fail sometimes.

The location appears to immediately after raising, and then confirming, a modal dialog.
  Then shortly afterwards, when looking for this relatively straightforward xpath:
 "./descendant-or-self::*[contains(normalize-space(.), 'Song 0')]",  I get this exception:

[Exception... "Component returned failure code: 0x80070057 (NS_ERROR_ILLEGAL_VALUE)
[nsIDOMXPathEvaluator.createNSResolver]"  nsresult: "0x80070057 (NS_ERROR_ILLEGAL_VALUE)"
 location: "JS frame :: resource://fxdriver/modules/atoms.js :: <TOP_LEVEL> :: line
2361"  data: no]

I see this error in a number of different projects.   I've observed it in both version
2.5 and 2.7.

I can try to produce a minimum reproduction case, but at the moment I'm seeing this
in Rails applications using capybara and ruby selenium-webdriver.  It tends to happen
more when large numbers of tests are being run at once, so I'm not confident a minimum
case would actually reproduce it.   Timing issue, perhaps?

The capybara code that triggers it in one project looks like this (we're using an rspec
plugin that maintains state between examples in sequence):

  it "when I click destroy " do
    within "#track_#{@track.id}" do
      click_link "Destroy"
    end
    # accept the confirmation dialog
    alert = page.driver.browser.switch_to.alert
    alert.accept
  end

  it "should no longer show the track in the list" do
    page.should_not have_content(@track.name)
  end

I'm also having this issue with Ruby 1.8.7, Capybara and selenium-webdriver. I've tested
with versions 2.6.0 and 2.7.0, and both have this problem.

The error appears for me intermittently on the following lines:

page.should have_content(text)
fill_in(field, :with => value)
click_link(link)
choose(field)

Is this issue fixed? I'm facing the same problem... 

FYI,

here's another version of a fix for Capybara:

https://gist.github.com/1137135

This issue was closed by revision r14381.

Which version of selenium-webdriver ruby gem will incorporate this fix? Is there any
page with release notes for each version of selenium products?

This will be in the 2.10 gem which should go out this week. You can find the Ruby change
log here:

http://code.google.com/p/selenium/source/browse/trunk/rb/CHANGES