Just ran into this and wanted to share with everyone.  I have NCover integrated into our continuous integration server.  I use it for informational purposes only.  In other words the build does not fail if coverage drops below a certain percentage.  A recent forced password change caused the CruiseControl.NET service to stop working as it was running under my account.  The reason it was running under my account is that I'm an admin on that machine and NCover.Console.exe requires admin privileges to run.  If you don't run under an admin account, the build server will work fine until it tries to run ncover, and then you get a deceptive error that can lead you to start looking in all the wrong places:

At least one test failed under code coverage.\r\nExternal Program Failed: c:\dev\ccnet\WebSite\build\tools\ncover\ncover.console.exe (return code was 1)

So rather than tying the service to my account I've gone ahead and created another account with admin privileges which is set to never have the password expire.  I don't like having the CruiseControl.NET service running off an admin account, but as far as I can tell it's the only way to get NCover to work.