I encountered the same problem after upgrading to Lion. If the cause of your issue is the same as the cause of mine, it is because you no longer have write permissions on your autosave folder.
Set the finder to show hidden folders and files by opening the Terminal and entering the following:
Code:
defaults write com.apple.Finder AppleShowAllFiles YES
Restart the finder by holding 'alt' and right mouse clicking Finder on the dock, then click
Relaunch.
Browse to your autosave folder. It should be located in
username / Library / Autosave Information. If there is a small red icon on the folder, it means you've got a permission issue.
Get Info on the folder and then fix the permissions. Either allow
Read & Write access to everyone or, if you share the Mac, add your user to the permissions lists using the small + and give it the correct permissions.
Autosave should now work properly again.
You can hide the folders and files using the same command as you used to show them, but replacing
YES with
NO. Relaunch the finder again to apply the change.