Może to rozświetli trochę sytuację.
O ile zrozumiałem to potwierdziło to, słowa Picasso.
This problem is with DNS. Our DNS servers don't have an IP address for that website server name (www.nasza-klasa.pl).
We've no reason to suspect that this is any fault with our DNS servers.
One part of the problem seems to be that one of the nameservers for nasza-klasa.pl is not accessible from here, as shown in this traceroute:
Tracing route to ns0.nasza-klasa.pl [188.8.131.52]
over a maximum of 30 hops:
1 <10 ms <10 ms <10 ms router [10.0.0.15]
2 22 ms 22 ms 22 ms lns2.net.imagine.ie [184.108.40.206]
3 22 ms 22 ms 22 ms ve5.core.net.imagine.ie [220.127.116.11]
4 22 ms 22 ms 22 ms ge0-0.border1.net.imagine.ie [18.104.22.168]
5 23 ms 22 ms 23 ms ge-2-0-0-207.dub20.ip.tiscali.net [22.214.171.124]
6 46 ms 46 ms 46 ms so-5-0-0.fra40.ip.tiscali.net [126.96.36.199]
7 47 ms 62 ms 61 ms netdirekt-gw.ip.tiscali.net [188.8.131.52]
8 47 ms 48 ms 61 ms 89-149-218-18.internetserviceteam.com [184.108.40.206]
9 89-149-202-174.internetserviceteam.com [220.127.116.11] reports: Destinati
on host unreachable.
Our DNS servers won't be able to get the answer from that server.
Another part of the problem is that the TTL value for the A record for www.nasza-klasa.pl is just 120 seconds. This means that when our server has an IP address for that host name, it can holf it for just 2 minutes, after which it must ask again.
Although this is not the cause of the problem, it makes the problem harder to investigate, as much of the investigation we do gets out of date in a couple of minutes.
Since you were actually able to look up the IP address when you were doing the traceroute, it seems that the problem is intermittent, which again makes it more difficult to diagnose especially when the TTL of the A record is just two minutes.
We'd recommend contacting the host of that domain and explaining this to them. They might be aware of the DNS problem or might be able to make change(s) to DNS to work around the problem.
Imagine Technical Support