After running Microsoft Web Test Recorder fpr the first time Internet Explorer regularly shows 404 error if a website does not response very quickly. This is common in development as a break point can prevent the server responsing to the client until to server continues, but this can also occur on other sites.
Running internet explorer in "no addins" mode works fine, but in normal mode 404 errors are annoyingly common. There does not appear to be any way of removing the web test recorder plugin. All other web browsers work fine as i have not used these for testing.