When I check one of my sites with Xenu link sleuth, I get a long list of addresses with an "error code: 12029 (no connection)". When I click on the items, they invariably open without problem. I've never come across this behaviour before with this site and have not seen this code on any of my other sites. (Of course, I checked some others, thinking there might be something wrong with my own internet connection).
Does anybody have an idea what could be the reason? Do I have to worry about it (apart from the fact that it is difficult to spot an actual 404 in this mass of 12029s)?
That error code is an internal Link Sleuth error code -- It certainly is not a standard HTTP/1.0 or HTTP/1.1 "internet error code." You might want to try a search for Xenu 12029 -"broken link report" [google.com] to see if anyone else has run into the problem.
Xenu opens hundreds of simultaneous connections, and it may be that the TCP/IP stack on your computer is not configured to support that many connections. I've seen that setting somewhere in the Windows Registry, for example. Also, your firewall or your ISP's firewall may limit the number of permissible connections. Same for the remote host you're trying to check. Or maybe that server is too busy to support a high number of requests at the time you're checking it (try again at 3am local time, unless your site has hundreds of global links).
So, this doesn't seem to be a special Xenu-Code. It's a German site and it is still quite early in the morning, - so I wouldn't expect much server load, - unless some bot is heavily spidering my site...