failed to refresh file loads empty

I'm got a dashboard with numerous graphics created by questions that relate to a csv file that I upload weekly.

Today I tried refreshing the csv file but it gives me a warning saying that the "last refresh failed" and the details 

The graphics now don't work as the file that has been loaded is blank.  I've opened the csv separately and it is not empty.  I can't work out why the file isn't loading.  It is a lot smaller than the 1gb limit.