formula stopped working

Hi. I am using a formula to copy data from one spreadsheet to another. The formula worked perfectly for several months and then a couple of days ago it stopped working. I checked tools>options>calculations and it was set to automatic. Any ideas? Thanks.

We're going need more information than that.

Post the formula in question
Describe "stopped working"
Does it get an error message now? What error?
Does it give the wrong result? What result DOES it give, what result did you expect, and why?

Perhaps even post a sample of the workbook.