Animate closes with the following message: Unknown error; quit application

that looks like you're trying to load a corrupted fla file.

if that occurs only when you try to open that specific file, try to repair it:

rename it to a rar

use winrar to repair it

rename the repaired rar to a fla

retry opening the fla

if that fails (expected most of the time), open AutoRecoverFilenames.txt* and see if there was a saved file and, if so, check the folder location listed

*

win:

C:\Users\<username>\AppData\Local\Adobe\<animate version>\en_US\Configuration

mac:

Users/<username>/Application Support/Adobe/<animate/flash version>/en_US/Configuration/

p.s  in the future, save your work periodically with increasing version number appended. for example, for project1.fla, save as project1_v000.fla, project1_v001.fla etc.  close and reopen the latest version to confirm it's uncorrupted.  only then can you delete the previous versions.  (and don't save over that confirmed version.)