Have you tried going to
Tools -- Options -- [Calculation] tab and ticking the box labeled
"Iterations"? If that box is checked, then circular references are allowed
in the workbook. I don't know why they call it 'Circular Reference" at run
time and "Iterations" in the [Calculation] tab, but they do. Might have been
more 'intuitive' had they labeled the box on the [Calculation] tab something
like "Permit Circular References".

"turbosteve" wrote:

With complex calculations that require a circular reference, you can have an
error when you open the spreadsheet. It can be fixed by replacing a key value
in the reference to get the calculation going, then put the real calcuation
back in. This is cumbersome--how can you provide a way for the circular
reference calculations to start?