No, it is most likely because your site is loading some object - like urchin.js from google-analytics.com - that a lot of other tests have been loading also. That means that our security checks will think someone is trying to DOS google-analytics.com and so stop your test. We have a list of exclusions that the system should not bother checking (such as google-analytics.com) but the list is not complete so people run into this problem frequently right now.

I am going to fix so that we inform people what the offending URL/object is (rather than just saying "one of the systems involved in the test..."), so they can remove it from their load scripts (if you're a registered user you can edit your load scripts before starting a load test) and also contact us and ask us to put new systems into our exclusion list.