"Why link it then?", you may ask. To see how many people try to follow it. Bad cross-references (just like other searches) get added to the list of frequently requested missing terms each time someone tries to follow one. This allows me to see either that the link was really bad (e.g. mistyped), or that it is worth adding a new definition. "Why don't you just fix them all?", you now ask. Because there are a lot and I don't have time. This way I can spend my time on the ones most people want.
So, please don't tell me if a cross-reference goes nowhere or returns "not found" (unless it is obviously mis-spelled). I already know and will fix it eventually.
If you get an error like "host unknown" or "host unavailable" this may indicate a temporary problem so, if possible, please try again after an hour or next day before reporting it as a bad link.