"ChangeLink" method in Excel fails

I have a set of Excel files that I am archiving, using code to simply copy the entire "Active" directory to a dated "Archive" directory.  Several of these spreadsheets contain only "rollup" values: summed values from other worksheets.  In all but a single instance, the files from which the rollups derive their sums are in the same directory as the rollup file.  When I copy these to a different place, the links automatically update themselves.  The exception is a "rollup of a rollup": values from the individual rollups are themselves summed into a grand-total file.  Because the grand total file is in a different directory than the files to which it is linked, the links remain pointed to the "Active" directory instead of their relative counterparts in the "Archive" directory.  

When attempting to correct this using code, I get an error when running the "ChangeLink" method.  The error says simply, "Run time error '1004'.  Method 'Changelink' of object '_Workbook' failed."  The same action I am able to perform manually fails in code, with no explanation other than it failed.  

Your feedback, as always, is greatly appreciated.
Peter Ferber