Series function disappears from Chart series edit

I'm running Excel 2002-SP3 under XP-Pro SP3 (and later fixes)

I do simple VBA stuff, and fairly complex formula-based sheets with what I thought were dynamic named ranges.

For whatever reason, I've never done a chart with dynamic named ranges before, so I tried.

The "series" function would not appear in my formula edit line when I clicked on an axis in a chart "series" window containing a named dynamic range (one I had created).

So I downloaded an example, tried editing the Series in the chart, and it worked. The "=SERIES(xxxx) appeared in the function editing line and the X-series line in the chart SERIES tab, and I could change it successfully.

Then I loaded up my spreadsheet, and trying the same, it didn't appear in the formula line.

Going back, now the example that worked also won't display SERIES in the function editing line, and it is stuck that way. I never saved the working example, and re-downloadiing it doesn't fix it either.

I know the SERIES function is not a worksheet function, only for charts. But why would it fail to appear, or worse, appear for a few tantalizing minutes, then never come back?

Is there a registry entry or configuration item that changes to cause this? I really need that function, and cannot access it now. Presently, nothing I enter into a chart series is treated as dynamic range, and it always reports an error in the formula when I try.

Thanks,
LLoyd