[lippe_maia]

One thing I would do is figure out whether they got some information about you that made them not want to bring you on or whether some disruptive event happened at the company. If there some information or misinformation out there that would cause someone to rescind a job offer, it's very important that you know about it.

Beyond that, it seems like you should find a job at another company or try to get your old job back. A lawsuit seems really complicated and unlikely to get much for you.

[dotBen]

It's a nice idea and worth asking but many employers are loathed to give critical feedback these days for fear of being sued (and even more so if they rescinded the offer and so the individual might have a case for damages)