Error message #N/A appears in linked cells

Hello,
I'm using Excel 2003 and have files with lots of links. Cells are linked to
an external workbook. The cells in the same column have inconsistent link
results. Some cells display #N/A and some cells are fine. The formulas are
the same, except they refer to a cell in a different row. When I open the
supporting sheet the cells update fine and the #N/A disappears and I get the
source data. When I close the supporting workbook the #N/A returns. The
cells are linking text data.
Would anyone know what is causing this and how I could fix it?
Thanks,
Jake