Losing formula references to other sheets - HELP!
 

I have a spreadsheet that has dozens of references to other sheets in the
formulas...like so:

=IF(OR(ISNA(VLOOKUP("SLATE",'G:\GS_Secure\REPORTS\ Monthly\HiPath\USER_SUMMARY\10\[USER_Summary.xlsx]USER_SUMMARY'!$A$9:$D$12,2,FALSE)),ISBLANK(VLOOKUP ("SLATE",'G:\GS_Secure\REPORTS\Monthly\HiPath\USER _SUMMARY\10\[USER_Summary.xlsx]USER_SUMMARY'!$A$9:$D$12,2,FALSE))),"",VLOOKUP("SL ATE",'G:\GS_Secure\REPORTS\Monthly\HiPath\USER_SUM MARY\10\[USER_Summary.xlsx]USER_SUMMARY'!$A$9:$D$12,2,FALSE))

When I save the workbook and re-open, the formulas change like so:

=IF(OR(ISNA(VLOOKUP("SLATE",'C:\Documents and Settings\RRoss\Application
Data\Microsoft\Excel\HiPath\USER_SUMMARY\10\[USER_Summary.xlsx]USER_SUMMARY'!$A$9:$D$12,2,FALSE)),ISBLANK(VLOOKUP ("SLATE",'C:\Documents
and Settings\RRoss\Application
Data\Microsoft\Excel\HiPath\USER_SUMMARY\10\[USER_Summary.xlsx]USER_SUMMARY'!$A$9:$D$12,2,FALSE))),"",VLOOKUP("SL ATE",'C:\Documents
and Settings\RRoss\Application
Data\Microsoft\Excel\HiPath\USER_SUMMARY\10\[USER_Summary.xlsx]USER_SUMMARY'!$A$9:$D$12,2,FALSE))

What is causing this and how do I stop it? This never happened in the old
version (XP) of Excel, but this new 2007 does it all the time.

Thanks!