Which version of Word/Excel? Has anything obvious changed (e.g. upgrading to
Word 2003 SP3?)

For a temporary fix I would try the DDE option at
http://tips.pjmsn.me.uk/t0003.htm, or if the workbook is simple (e.g. all
data and no formulas, try exporting to .csv and re-importing into a brand
new workbook.

However, if you have done anything like
a. add rows which happen to have cells formaated as "date/time"
b. add 8 or more rows at the top of your sheet that have date/time values
in them (doesn't sound likely but you never know)

that's probably the cause of this problem.