Does the document have any macros in it? I once saw a similar message when trying to load an Excel workbook; the workbook had an embedded or autoloaded macro, stored in a separate file which got moved and later could not be found.
The error message did not say anything about the Macro, the error message blamed the workbook file. Just a thought. Remember the old joke about the lost helicopter pilot who asked where he was? "You are in a helicopter" was Microsofts answer. Your error message might mean that the whole document "G:\purpose.doc" is not wholly valid because it is incomplete.
Also, can you recover the backups? Is this a fast saved file?
Sigh... M$ - so many ways to get you to buy the newer stuff.