Fei is right, the message cannot be changed. BUT fortunately you could produce a "calculation condition not fulfilled" condition which error message could be customized. E.g. I add the expression directly in the calculation condition. When it returns null, the condition is not fulfilled and I could make use of the custom error message box.
You can use a text box with your message to hide your graph when data is null.
Make a copy of bar graph in different sheet and convert that chart type from General tab to Straight Table.
After then you can use macro for this table (say CH16):
ActiveDocument.Variables("v").SetContent cell.text, True
This will store the total (which is 0 whenever "no data to display" comes) of your expression in variable "v".Then you can use this v variable to show/hide your text box.
Hope this helps
Yes, you have to make some button to run macro. But to run this automatically on the basis of user selection , apply triggers (to Run macro) on all columns through which data of that table (CH16) changes.
Note: in my table cell(1,4) contains total. For getting this value , check "Expression total" instead of "No Total" under expression tab