Karen,
I created custom profile integer fields for Risk and Return and then created the bubble chart from these fields. It works just fine. The field has to be numberic (interger or decimal). The Project Name field is in the Series, X axis is Project Return [1=Low to 5=High], Y axis is Project Risk [1=Low to 5=High], and bubble size is budget. This works great. Remember to turn on tooltips to give the project name and information when you hover over a bubble.
John F. Filicetti, PMP, MBA