dfu genpkg exits with "ValueError: tobinarray: wrong value for size"

[datachomper]

I'm just trying to build one of the example apps for the beacon kit and I'm running up against this cryptic error when trying to use dfu genpkg to build an application only firmware zip. Using Master Control Panel v3.9.0.6

Any ideas?

[datachomper]

raw.githubusercontent.com/.../blink.hex