You are asking a very technical question that may have many interpretations depending on the facts of your case. I would not rely on any advice on this forum, and instead would seek a title insurance policy by a top rated title insurance company.
That said, MERS is a database for which banks/servicers/note-holders belong to... rather than recording each time the note and or deed is assigned to another, they recorded to MERS, and MERS keeps track of who it is assigned to... then if there is a transaction that warrants it, they record the last transaction with the county.. supposedly they get around the legal requirement of recording the assignments because they all belong to the MERS entity... There are many legal theories for and against it... since it is so popular and big in the system, most courts go along with it, otherwise it would destroy the system and create chaos.. however there are some judges that rightfully so (I think) question the validity of the transaction and title chain...
If you cannot get a title insurance policy, you may have to go to court and file a "Quiet Title Action" suite where the court would rule and clear all title issues.
I hope this helps you, if you like my answer give it a Thumbs Up! or select it as the Best Answer.