'saving' and 'undo'

Me too, the same problem. Can't save (High Sierra 10.13.5, CC 2018). Changing the file name did not help. Packaging of files not possible. At first, InDesign said something like "not enough disk space", but 217 GB are free.

I'm having the same problem...Just lost about 2 hour's work because I could neither undo or save. Did anyone ever find a solution?

Have you tried trashing your InDesign preferences? Doing so will reset the program to default and hopefully solve the problem.

To do so on a Mac:

With InDesign closed Launch a Finder Window in column view and click on your home folder. With the Option Key pressed choose Library from the Finder Go Menu. Within the Library folder find the folder called Preferences and within it find the following two files and delete them: “Adobe InDesign” and “com.adobe.InDesign.plist”. When InDesign is next launched it will create new preference files and the program will be restored to its defaults.

After you’ve reset up the program (make sure that no document window is open) to your liking, you can create copies of your personalized “mint” preference files (make sure that you quit the program before copying them—that finalizes your customization) and use them in the future to replace any corrupt versions you may need to delete.

Undo is only available when you did something. When there is no previous action this function is grey.

The command Save is no longer available when you just saved the document. Do something new and you can save the document again.

Hope this answers your question.

Groeten uit Eindhoven