Also, what format are the dates in?
Sometimes the unreliable piece of junk aka as Excel makes confusion
between the European and the American format: for example, when
reading the date '20/1/2007' it might not recognize it as European
format, and return an error because the calendar does not have 20
months.

On Aug 8, 4:31*pm, "Peo Sjoblom" wrote:
Which date function? If you are using things like EDATE then you need to
make sure the ATP (Analysis ToolPak) is installed and selected under
toolsadd-ins, you might need the installation CD for this.