Sorry my english, it's not my native language.
Flash CS6 was crashed and when I trying to reopen .fla file, it shows error dialog "unexpected file format". How I can repair this file?
rename its extension to zip and try to unzip it to extract its assets and add to a new (uncorrupted) fla.
failing that, use a zip repair to try and repair the zipped file so you can unzip and extract its contents.
failing that, use a decompiler to decompile a working swf to a working fla.
and, whether that all fails or not, learn a lesson about creating sequentially named backups so you never lose all your work again ( project_01.fla, project_02.fla, etc)