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.
