Error 3013 trying to re-save a file

This is a Windows issue only.

I have an AIR app that writes an XML file to the users hard drive. If they input the data and press SAVE everything is fine. If they then change their data and press SAVE again overwriting the file I get an error 3013: "File or directory is in use."

I'm creating a fileStream, opening Async, write UTF Bytes and then closing the file. Am I missing a step?

(With this project the user is not allowed to change the file name, it needs to match the flv file name.)

Any suggestions are appreciated.