Leaving out 'be' and other verbs in headlines is characteristic of the genre -- perfectly normal and standard for (shortened) headlines anywhere; web, newspapers, magazines A BBC World English expert gives examples / further explanation: http://www.bbc.co.uk/worldservice/learningenglish/grammar/learnit/learnitv327.shtml Here is another example: http://www.theguardian.com/uk headline >>> Juncker (is) under new pressure over tax We know it's there, it can be omitted to save space without interfering in understanding...it's a convention / very standard

We never really omit the word "is". Computer errors is perhaps the only case where we do so on a regular basis. In fact in this case it's almost more normal than including it. I can't think of any other situation where it might be omitted though. In this respect English is almost opposite to Russian :-)

Because it is written incorrectly. If it is to be a sentence. It should have the "is" and a "the" The repository is unavailable because of the ..." As a notice on a web site this is fine. It's just a shortened form.