I guess you are attempting to use the “Uloz.to Manual Download” method? From what I’ve seen, that method has always been a little buggy.
For what it’s worth, I recommend using the “Multipart RAR Download” method. Seems like people run into fewer problems with it, and you get the same product in the end result.
The guide with links to the rars for that is here:
https://goo.gl/5Sif60