Tests fail sporadically using CruiseControl.NET with NUnit: error 800704a6 - nunit

Question

My partner and I have a suite of tests running nightly on a build server for our project. We use CruiseControl.NET to run the server, and the tests are written using WatiN and NUnit. We have CruiseControl.NET running as a service with access to interact with the desktop on a local system account. Every few times that we run a build, certain tests will fail with error messages such as the following:
Test: cfarmweb.tests.Views.GeneralRegressionTest.DuplicateUsernameTest
Type: Failure
Message: SetUp : System.Runtime.InteropServices.COMException : Creating an instance of the COM component with CLSID {0002DF01-0000-0000-C000-000000000046} from the IClassFactory failed due to the following error: 800704a6. TearDown : System.NullReferenceException : Object reference not set to an instance of an object.
at WatiN.Core.IE.CreateNewIEAndGoToUri(Uri uri, IDialogHandler logonDialogHandler, Boolean createInNewProcess)
at WatiN.Core.IE..ctor(String url)
at cfarmweb.tests.Navigator.SiteNavigator..ctor(String browserName, Boolean visible) in c:\ccworkdir\CFarm\builddir\cfarmweb.tests\Navigator\SiteNavigator.cs:line 35
at cfarmweb.tests.Views.GeneralRegressionTest.MakeNavigator() in c:\ccworkdir\CFarm\builddir\cfarmweb.tests\Views\GeneralRegressionTest.cs:line 34
--TearDown
at WatiN.Core.Browser.OnGetNativeDocument()
at WatiN.Core.DomContainer.get_NativeDocument()
at WatiN.Core.Document.ContainsText(String text)
at cfarmweb.tests.Navigator.SiteNavigator.HasText(String target) in c:\ccworkdir\CFarm\builddir\cfarmweb.tests\Navigator\SiteNavigator.cs:line 213
at cfarmweb.tests.Navigator.SiteNavigator.SignOut() in c:\ccworkdir\CFarm\builddir\cfarmweb.tests\Navigator\SiteNavigator.cs:line 110
at cfarmweb.tests.Views.GeneralRegressionTest.DisposeNavigator() in c:\ccworkdir\CFarm\builddir\cfarmweb.tests\Views\GeneralRegressionTest.cs:line 123
The success of the builds does not seem to be dependent on changes to the code itself, as we have had builds break or be fixed after changes to parts of the program that are unrelated to the tests.
We are both new to the field of software testing (and development in general), but nothing we've found online about this error seems to pertain to our situation. We've seen everything from a system reboot pending to compatibility issues with Internet Explorer 8 to JavaScript errors, but nothing we've tried has fixed the issues. One of the most difficult parts is that it's not consistently reproducible. How can we fix this problem?

Answer 1

Ben,
I had the exact same issue, surprisingly enough...I think I have the solution. It appears to be a threading issue. The [RequiresSTA] tag at the top of a test is meant to create each test to be single-threaded by implicitly placing the tag [STAThread] on each method. However, I am inclined to believe that these tags are not being called on the [SetUp] or [TearDown] methods, creating threading issues. I have hopefully resolved the issue by placing the [STAThread] tag on each method (including the [SetUp] and [TearDown] methods) explicitly. I will let you know of any further changes, but it's worth a shot.

Answer 2

There are some similar issues related to Watin and IE8.
Running Watin on TeamCity
failed due to the following error: 800704a6 while trying to read data from a text file in teamcity
https://serverfault.com/questions/179156/ie8-script-error-800704a6
From what i understand, make sure you windows is fully updated, make another restart just to make sure and check if problem persist.
If it does, try runnning ccnet not in service mode.
If still no good, try to play with internet options security to determine if this affect the problem.
HTH