Unexpected format means that the original fla file is created in the advanced version. Now you'r opening that file in the older version. Convert it from the advanced version to the old version which will open your file.
No i was working on the file in flash cs5 and i am trying to open the file in flash cs5. This is the case of a corrupt file while flash cs5 was saving and not wrong version opening.
Did you save your file on a Network ? What were the last few steps before saving and closing the file .
Can you please email your fla to us at mailto:FlashAuthBetaBugs@adobe.com? Please note that our filter system cannot accept .zip file. If you are to zip your fla, please change the file extension from .zip to .zzz.
Flash Authoring QE
My file was on a network however there were no network disruptions. I repositioned a movieclip on the stage, saved the file and then the application crashed during the save.
I have just emailed the file across.
Today we have released Flash CS5.5 update . This update contains fixes for opening and saving some Flash Professional files (FLAs) in CS5.5, and other bug fixes.
Please download Flash CS5.5 updater .
You Can download from Flash > Help > Updates .
Please read the following blog post for a solution to the Unexpected File Format Error: