Well since my neighbour [CENSORED] at computers I changed his
Workgroup name instead of mine.
FYI. Everything seems to work just fine now even though I don't have DNS Proxy. It turned out that my router was broken (it shut down itself every 5-10 minutes and restarted). I changed to a new one of same model
and the same firmware
I've also changed the name for the workgroup and that also works perfect. The 450X2 finds and plays everything.