Quote Originally Posted by AlexLeo View Post
I do not think that such an approach is correct from a legal point of view.
You mean revoking a licence? If there is some clause like that in the agreement then I don't know what could be illegal in making use of it. That's a standard sentence that you have to accept (and obey) the licence to be able to use the product. If the licencer claims (and proves) the licencee didn't/doesn't obey it, use of the product has to be stopped.