I have a worksheet (.xls) that holds data and built some pivot tables out of
it. It worked fine till today. The pivot tables were able to refresh with new
data. After saving it and re-opening the file all the pivot tables turned
into values. That is, all the pivot tables are now static values. I repeated
the process and the result is still the same. What could be the problem and
how to resolve this?

I am using Excel 2007.