I run an education-based website and have been offering users free downloads of one of our ebooks, as a promo thing for one week only. I was happy with the uptake at first. I noticed that on average around 1500 downloads were made each day. However, when I double-checked the logs I noticed that up to 80% of the downloads were unsuccessful. Visitors had started downloading but either given up or been unable to download the files. How can I make the experience more successful for visitors? These were only small-ish files, between 5-6 MB (.PDF files).

Many thanks!