The way you worded it before, you made it sound like you couldn't sue over a copyright that was transferred to you. I don't believe that's true.
What is being said in the Rightshaven case is that you can't transfer just the right to sue without giving them any of the exclusive rights protected by copyright. I believe that, had they transferred the whole copyright, or at least some of the exclusive rights protected by the copyright, Rightshaven would have had standing to sue.
In short, I believe that bluedanieru's formulation is the correct one. IANAL, though, and this kind of stuff turns on hair-splitting interpretations of words.
I read the decision linked by Groklaw as I recall but can't find it right now.
Judge Pro ruled you could not sue for copyright infringement if you weren't the holder of the copyright.
Judge Hunt ruled that you could not transfer enough copyright to sue but not all copyrights.
I've not completely Sheperded that case but I'm coming up blank on any appeals for those particular points.