"Build Health" viewlet shows no data

I've added the "Build Health" report viewlet. I have picked a build that we've done probably 20 builds for in our RTC install. However, the viewlet always states, "No build results were found." In contrast, I've also added the "Builds" viewlet (which gives a textual list of the previous few builds), selected the same build, and I get the results I expect in that viewlet.

Any idea what's going on with the "Build Health" viewlet?

Thanks in advance,
Mike Johnson