When we save project the Soundpool's folder path, the project folder path should remain same. Any changes in the path will be result of error. In this case it seems your Windows XP Music Maker folder path and Windows 7 folders paths are different that is why you are getting error.
If you remember the folder paths of Windows XP try to set accordingly in Windows 7.
Other than above, I hope you are also aware that the Windows 7 operating system is compatible with Windows XP systems and some programs needed to be run in XP Compatibility Mode: You can read about it using url link.