reference errors linking to other workbooks

Hi All,
I have a co-worker who created a spreadsheet with several worksheets and lots of formulas dealing with net pay. He asked me the other day as to why his spreadsheet won't work on one computer and works fine on another. Most of our work sites have at least 2 computers, Win XP Pro, Office 2003 Pro. He created the spreadsheet on computer A, when he tries to open it on computer B - at the same work location, he gets lot's of !REF errors. Macros security is set to Low. He sent me the spreadsheet, I get the same errors.

Any ideas why??

Thanx...LT

Macros security is set to Low.

That is an invitation to deep heartbreak.