Debugging import on nopCommerce 2.65

Hello,
I have a C# program that takes data from a database and creates an XLSX file which I then attempt to import into nopCommerce.

This is the error I get attempting to import the XLSX file into nopCommerce 2.65:
Object reference not set to an instance of an object.

And this is the link to the latest XLSX file I generated and attempted to import:
https://docs.google.com/file/d/0B0xs2YFff_jOalpLS2ZKNjdHN0k/edit?usp=sharing

Is anybody able to spot what's wrong with my XLSX file?

Additionally, is there any way to have a more precise indication as to which is the exact field which is failing, if any?

Ideally, I would like to be able to spot the exact failing field from, say, a log on a production installation (not in a localhost debug installation) - where can I find such a log after an import process, assuming there is any?

Thanks for your attention,
Francesco

Yes there is a log under the systems panel that will tell you what the error is in a little more detail than the products screen. But it isn't very detailed. I think it has something to do with the type of data in the field and/or something else. Im doing the same thing and the only time I get a successful import is when I import the data that I exported from the export all function. Not very useful