I thought I will just confirm that I had the same problem:
1) used UnetBootIn from Linux to install the iso onto a USB stick
2) my installation gets stuck at package manager update download - error being 'download failed'
3) If I skip that step, I get stuck at a subsequent step 'grub-pc' installation failed
Reading a suggestion posted above, I tried using 'win32diskimager' from windows and the installation finished smoothly and succeeded without any errors.