Illustrator Files won't open after downloading or syncing back to my Mac

[Bsmalldesign]

I just went into my dropbox and synced/downloaded some Illustrator files from last year. The dropbox preview shows the file and the finder shows the thumbnail for the file. All of the linked files/fonts are in the same folder where they were packaged together last year. I try to open one of the .AI files and get the error: "Could not open the file because the plug-in could not understand the file". I also would sometimes get an ANSI encoding popup where I would have to choose the type of encoding I want, even though I created the files in Illustrator on this same computer. This is frustrating because now I can't work on the files.

[Bsmalldesign]

Also, I can open/see the files perfectly if I open the AI files in Photoshop (but of course I don't need them opened in Photoshop, I need them in Illustrator, haha).

[Bsmalldesign]

Looks like somehow when Dropbox synced, it corrupted all of the placed/linked image files because I can't open those in Photoshop individually. When I delete them from the linked folders, I'm able to open the AI file. But now I have to re-source my images.