How To Chart A Formula in Excel 2007

I'm looking to plot multiple formulas on a single chart, and came across a
thread from 8/12/2005 for earlier versions of Excel for a single function,
which causes errors when recreated in 2007.

Error is
A Formula in this worksheet contains one or more invalid references
Verify that your formulas contain a valid path, workbook, range name, and
cell reference

I presume its due to changes in 2007, and possibly the Evaluate formula as I
cant find it listed in 2007.

Is there a new technique that avoids the error?

Thanks Very Much for any help.

Kris