InDesign preferences can become corrupt when the InDesign application quits unexpectedly or when you force quit InDesign. One consequence of this is that the Save, Save As, or Export entries in the InDesign File menu may become unavailable for selection.

If this should occur, you can resolve this by resetting your InDesign preferences. For instructions, see How to reset Adobe InDesign preferences.

For more details, see the following page in the online Adobe InDesign User Guide: Restore all preferences and default settings