[QGIS-Developer] Error in zonal statistics?

[Martino]

Dear Colleagues

I am attempting to use the zonal statistics tool of QGIS. 

I am overlaying a vector layer containing zones on a raster layer that
contains temperature data. When I use a climate raster layer from
WorlClim (http://worldclim.org/version2) everything works as expected.

However, when I use a climate raster layer from 

https://utexas.app.box.com/v/Xavier-etal-IJOC-DATA

the process does not run and I receive the error message

'unsupported operand type(s) for *: 'float' and 'NoneType' See log for
more details'

I don't know what this means but a Google search suggests this is a
Python message, and this is why I am sending this query to the QGIS
developer list (please forgive me if I have erred). 

I would be grateful if anybody could instruct me how I could delve into
this matter further, with the aim of resolving the problem.

With grateful thanks!

Martino