My master pages have disappeared from the View menu in Frame Maker and I can't get to them. View does show body pages and reference pages.

Master pages went missing from my FrameMaker 12 setup about 4 days ago. I can see body and references pages. I have tried reinstalling. The master pages are missing from all of my FrameMaker documents, absolutely all of them. I have done two new installations of FM 12, no fix.