#REF errors in links
 

I have a workbook with links to many worksheets in separate files. Each year
I used to change the source files to the corresponding year and the links
work fine. Now all of a sudden this year when I change the source file the
links shows #REF. I don;t know?Why.But the formula is displayed correctly and
the result is shown as #REF.Some one may help.
srinivasan