I'd get advice from an employment lawyer right away, sounds quite dicey your situation, I'm sure your manager had to fill out a bunch of forms and give specific reasons to put you on a 30 day review. Can you find out what those reasons were? Questioning the work of an 'expert' (was that person a contractor?) surely can't be an official reason to put you on review.

Also get your previous performance reports, that will hopefully show that whatever reasons he put down for placing you under 30 day review are out of character and unusual.

Edit: typos