"An error occured opening file ___"

then look for an auto-recovery file:

for win users, open C:\Users\<username>\AppData\Local\Adobe\<animate version>\en_US\Configuration\AutoRecoverFilenames.txt

and see if there was a saved file and, if so, check the folder location listed

for mac users, check the folder (for a file with name recover_) where the fla was saved. if the fla wasn't saved, i think you're out of luck, but you can still search your computer for "recover_"