Hm, not sure if you'll come back to read my post (your last login was 5 days ago) but I can tell you that the reason why it says "Failed to download" is because of your anti-virus program deleting bol.dll inside the BoL folder after you try to launch bol.exe.
To fix this, find the "correct" bol.dll. Download link can be found in the official BoL forum, try to google it since I got infracted last time I wanted to be helpful.
When you've finished downloading bol.dll, drag it to the BoL folder. Add an exception so that your anti-virus program doesn't automatically delete it.
I also read that you might have to move the whole BoL folder (along with the new bol.dll) to %appdata%. I had the same problem as you before but I fixed it this way.