After selecting the graph, I then select data under Object>Graph>Data. The window comes up, but no data - to modify!!
Are you sure that the diagram hasn't been ungrouped?
.Thanks for your quick answer!! Attached is the CS5 graph, and a screen shot of the new numbers. Good luck!!
You can't attach this here.
But actually you can also check that yourself. The layer panel will tell you if it's a diagram or not.
If at any point you saved the CS6 file down to CS5 and seen the message below, then the graph is now not a live graph anymore but has been turned into vector paths.
If you select the graph and can see
then you should be able to edit the data.