Do you file structure like this on dl server
http://1.2.3.4.5/csgo/maps/ put maps in maps folder
On cfg do
http://1.2.3.4.5/csgo
On server.cfg add
sv_allowupload "1"
sv_allowdownload "1"
If you follow this shud 100% work, but if not there might need additional configuring on dl server itself, perhaps a filesize limit on you're uploads or ttl for connection too short. Can be a couple of issues!
You have also mixed files in plain bsp and bz2 on your server try to convert all of them into bz2 with 7zip > ultra to save space and faster downloads.