Version 2.2 has been released to allow easier use with AVRStudio 6.
If your Project Designer folder contains a file ending with '.aps' then you delete it.
Regenerate your project in Project Designer making sure that you tick the option to 'Create AVRStudio project file'. This will create a fresh '.aps' file.
To use the project in AVR Studio 6 you should use the "File", "Import", "AVR Studio 4 project..." menu option.
In the pop up window, in the 'APS File Location' section, Browse and select the '.aps' file generated above.
Click the 'Convert' button.
That's it - you should now have an AVR Studio 6 project solution.