Change the font used in the Excel chart to something else on your machine. Right-click on the chart and select Format Chart Area. Go to the Font atb (at the bottom) and change it from Calibri (Theme Body) [Or whaterver it says] to something like Arial. Then recopy and paste the chart.
Bless ye, sir. That did the trick!
Weird, because I have that font (yep, it's Calibri) and I can choose it and use it in AI... but I changed Calibri to Arial in Excel, as you suggest, and I'm able to paste from Excel.
Thanks very much!