Just so you know, most of the active posting occurs on the last page. alot of times if you respond to an old post, you may not get an answer. this forum is not set up to view chronologically by post, but rather by topic date. (when the thread was started).
As to your question, I think you would find it difficult if not impossible to base a lawsuit on getting pregnant, (unless your dr specifically told you that it was impossible-then you could try and sue him/her, but I imagine even if that were the case, it would be difficult to prove) Bayer does clearly indicate that Mirena is not infallable, as is any method of birth control.