InDesign may not support this file format message?

Question

What do I do when I get a Adobe InDesign may not support this file format, a plug-in that supports this file format may be missing message?

Answer 1

Do you understand the difference between embedded (all of the image data is stored within the file) and linked (what happens when you use File > Place.... where a pointer to the file stored in the file along with a screen preview)? You must deliberately embed images -- there's no way to do it automatically. Pasted graphics are also stored internally.
As to why it no longer works? Probably a write error while saving, especially if this is saved on a network drive. Writing 9 gb takes some time, if the file was really that big and isn't cross-linked to something else.
To keep ID file sizes down always Place images and graphics rather than pasting, and do a periodic Save As to remove old change data that will become useless file bloat when you close the file. I tend to add a version suffix when doing the Save As at any major change point, rather than overwriting the original, as it gives me an automatic backup chain and a way to go back to a previous version if I need to move in a different direction.
Do you have a backup?