I would suggest rebuilding it from an IDML file.
You could divide your file into halves to see if they both refuse to save as facing pages. If so, it’s probably not a bad page, which I’ve had happen at least twice in very complex files.
Also, you might try turning Allow Pages to Shuffle on if it’s off, or off if it’s on, to see if that makes a difference.
Rebecca
Hi Folks — I am having trouble with a small InDesign file, 20 pages, 6x9 inches. I have been working in it in single page view but put it in facing pages to see how it balances out. It will not save in Facing Pages view, the save selections are greyed out. If I revert facing pages to single view and then I can save.