b10 already contains final build of UC 2.3u4, so things will not magically get better on that account
It seems that we are having another bout of repository issues. As far as I can tell from all related forum postings, the issue is not necessarily that server URL is not reachable - in that case, bootstrap does exit rather promptly. The problem is that connection to the server gets intermittently lost once the bootstrap is already in progress. So, even pinging the repository before starting the download would not help.
The only apparent solution is to get server side back in order.