Here's a possibility:
http://support.microsoft.com/support/kb/articles/Q172/9/48.ASP
XL97: "Not Enough Memory" Opening a Workbook with a Chart
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SYMPTOMS
When you open a workbook in Microsoft Excel 97, the following problems may occur:
You receive the following error message:
Not enough memory.
-and -
In the active chart, text is missing from both the legend and the chart title. Also, some or all of the chart series labels contain the text "0."
CAUSE
These problems occur if all of the following conditions are true:
When you open the workbook, a chart sheet is the active sheet.
-and-
The active chart sheet refers to cells in a worksheet that contain formulas that refer to one or more user-defined functions.
-and-
One of the user-defined functions uses the Volatile method by using the following line of code in the function:
Application.Volatile
WORKAROUND
To work around these problems, use either of the following methods:
Before you save the workbook, click a worksheet or chart sheet that does not refer to user-defined functions. When you do this, you ensure that the active sheet does not refer to a user-defined function.
-or-Remove Application.Volatile from any user-defined functions that are referenced by the chart sheet.
If you cannot change the active sheet or modify the user-defined functions, you can temporarily correct the chart by following these steps:
Switch to the worksheet that is referenced by the chart sheet.
Press CTRL+ALT+F9.
This forces the entire worksheet to be recalculated. When you switch to the chart sheet, the title, legend, and series labels appear correctly. Note that when you close and reopen the workbook, the problems may occur again.