Adobe Illustrator is noted for marginal compliance with graphic image standards. Some of the standards permit "additional features" and AI seems to use a lot of them. Its "native" format is simply unintelligible to lots of other programs, and even when you save as another common format, AI seems to want to add it's own unique "flavors" to the specs.

Some other graphics programs will occasionally recognize that what looks like an "ordinary" TIFF file is actually an AI-TIFF file, and may tell you so before rejecting it (and sometimes crashing).

It's a wonderful program, but shouldn't be the only good graphics program in your arsenal. It's just "not fully compatible" with too many other application programs.

If you have another graphics program that can open AI-produced images with reasonable reliability, sometimes opening and resaving in almost any other program will remove (or at least blunt) some of the "AI features" so that you can use the image more generally. That's a work-around we used to use a lot.

John